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Climbing Plants

Charles Darwin

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The Movements and Habits of Climbing Plants

by Charles Darwin

January, 2001 [Etext #2485]

The Project Gutenberg Etext of Climbing Plants by Charles Darwin

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This etext was prepared by David Price, email ccx074@coventry.ac.uk

from the 1906 John Murray edition.

THE MOVEMENTS AND HABITS OF CLIMBING PLANTS

PREFACE

This Essay first appeared in the ninth volume of the 'Journal of the

Linnean Society,' published in 1865. It is here reproduced in a

corrected and, I hope, clearer form, with some additional facts. The

illustrations were drawn by my son, George Darwin. Fritz Muller,

after the publication of my paper, sent to the Linnean Society

(Journal, vol. ix., p. 344) some interesting observations on the

climbing plants of South Brazil, to which I shall frequently refer.

Recently two important memoirs, chiefly on the difference in growth

between the upper and lower sides of tendrils, and on the mechanism

of the movements of twining-plants, by Dr. Hugo de Vries, have

appeared in the 'Arbeiten des Botanischen Instituts in Wurzburg,'

Heft. iii., 1873. These memoirs ought to be carefully studied by

every one interested in the subject, as I can here give only

references to the more important points. This excellent observer, as

well as Professor Sachs, {1} attributes all the movements of tendrils

to rapid growth along one side; but, from reasons assigned towards

the close of my fourth chapter, I cannot persuade myself that this

holds good with respect to those due to a touch. In order that the

reader may know what points have interested me most, I may call his

attention to certain tendril-bearing plants; for instance, Bignonia

capreolata, Cobaea, Echinocystis, and Hanburya, which display as

beautiful adaptations as can be found in any part of the kingdom of

nature. It is, also, an interesting fact that intermediate states

between organs fitted for widely different functions, may be observed

on the same individual plant of Corydalis claviculata and the common

vine; and these cases illustrate in a striking manner the principle

of the gradual evolution of species.

APPENDIX TO PREFACE (1882).

Since the publication of this Edition two papers by eminent botanists

have appeared; Schwendener, 'Das Winden der Pflanzen' (Monatsberichte

der Berliner Akademie, Dec. 1881), and J. Sachs, 'Notiz uber

Schlingpflanzen' (Arbeiten des botanischen Instituts in Wurzburg, Bd.

ii. p. 719, 1882). The view "that the capacity of revolving, on

which most climbers depend, is inherent, though undeveloped, in

almost every plant in the vegetable kingdom" ('Climbing Plants,' p.

205), has been confirmed by the observations on circumnutation since

given in 'The Power of Movement in Plants.'

ERRATA.

On pp. 28, 32, 40, 53, statements are made with reference to the

supposed acceleration of the revolving movement towards the light.

It appears from the observations given in 'The Power of Movement in

Plants,' p. 451, that these conclusions were drawn from insufficient

observations, and are erroneous.

THE MOVEMENTS AND HABITS OF CLIMBING PLANTS.

CHAPTER I.--TWINING PLANTS.

Introductory remarks--Description of the twining of the Hop--Torsion

of the stems--Nature of the revolving movement, and manner of ascent-

-Stems not irritable--Rate of revolution in various plants--Thickness

of the support round which plants can twine--Species which revolve in

an anomalous manner.

I was led to this subject by an interesting, but short paper by

Professor Asa Gray on the movements of the tendrils of some

Cucurbitaceous plants. {2} My observations were more than half

completed before I learnt that the surprising phenomenon of the

spontaneous revolutions of the stems and tendrils of climbing plants

had been long ago observed by Palm and by Hugo von Mohl, {3} and had

subsequently been the subject of two memoirs by Dutrochet. {4}

Nevertheless, I believe that my observations, founded on the

examination of above a hundred widely distinct living species,

contain sufficient novelty to justify me in publishing them.

Climbing plants may be divided into four classes. First, those which

twine spirally round a support, and are not aided by any other

movement. Secondly, those endowed with irritable organs, which when

they touch any object clasp it; such organs consisting of modified

leaves, branches, or flower-peduncles. But these two classes

sometimes graduate to a certain extent into one another. Plants of

the third class ascend merely by the aid of hooks; and those of the

fourth by rootlets; but as in neither class do the plants exhibit any

special movements, they present little interest, and generally when I

speak of climbing plants I refer to the two first great classes.

TWINING PLANTS.

This is the largest subdivision, and is apparently the primordial and

simplest condition of the class. My observations will be best given

by taking a few special cases. When the shoot of a Hop (Humulus

lupulus) rises from the ground, the two or three first-formed joints

or internodes are straight and remain stationary; but the next-

formed, whilst very young, may be seen to bend to one side and to

travel slowly round towards all points of the compass, moving, like

the hands of a watch, with the sun. The movement very soon acquires

its full ordinary velocity. From seven observations made during

August on shoots proceeding from a plant which had been cut down, and

on another plant during April, the average rate during hot weather

and during the day is 2 hrs. 8 m. for each revolution; and none of

the revolutions varied much from this rate. The revolving movement

continues as long as the plant continues to grow; but each separate

internode, as it becomes old, ceases to move.

To ascertain more precisely what amount of movement each internode

underwent, I kept a potted plant, during the night and day, in a

well-warmed room to which I was confined by illness. A long shoot

projected beyond the upper end of the supporting stick, and was

steadily revolving. I then took a longer stick and tied up the

shoot, so that only a very young internode, 1.75 of an inch in

length, was left free. This was so nearly upright that its

revolution could not be easily observed; but it certainly moved, and

the side of the internode which was at one time convex became

concave, which, as we shall hereafter see, is a sure sign of the

revolving movement. I will assume that it made at least one

revolution during the first twenty-four hours. Early the next

morning its position was marked, and it made a second revolution in 9

hrs.; during the latter part of this revolution it moved much

quicker, and the third circle was performed in the evening in a

little over 3 hrs. As on the succeeding morning I found that the

shoot revolved in 2 hrs. 45 m., it must have made during the night

four revolutions, each at the average rate of a little over 3 hrs. I

should add that the temperature of the room varied only a little.

The shoot had now grown 3.5 inches in length, and carried at its

extremity a young internode 1 inch in length, which showed slight

changes in its curvature. The next or ninth revolution was effected

in 2 hrs. 30 m. From this time forward, the revolutions were easily

observed. The thirty-sixth revolution was performed at the usual

rate; so was the last or thirty-seventh, but it was not completed;

for the internode suddenly became upright, and after moving to the

centre, remained motionless. I tied a weight to its upper end, so as

to bow it slightly and thus detect any movement; but there was none.

Some time before the last revolution was half performed, the lower

part of the internode ceased to move.

A few more remarks will complete all that need be said about this

internode. It moved during five days; but the more rapid movements,

after the performance of the third revolution, lasted during three

days and twenty hours. The regular revolutions, from the ninth to

thirty-sixth inclusive, were effected at the average rate of 2 hrs.

31 m.; but the weather was cold, and this affected the temperature of

the room, especially during the night, and consequently retarded the

rate of movement a little. There was only one irregular movement,

which consisted in the stem rapidly making, after an unusually slow

revolution, only the segment of a circle. After the seventeenth

revolution the internode had grown from 1.75 to 6 inches in length,

and carried an internode 1.875 inch long, which was just perceptibly

moving; and this carried a very minute ultimate internode. After the

twenty-first revolution, the penultimate internode was 2.5 inches

long, and probably revolved in a period of about three hours. At the

twenty-seventh revolution the lower and still moving internode was

8.375, the penultimate 3.5, and the ultimate 2.5 inches in length;

and the inclination of the whole shoot was such, that a circle 19

inches in diameter was swept by it. When the movement ceased, the

lower internode was 9 inches, and the penultimate 6 inches in length;

so that, from the twenty-seventh to thirty-seventh revolutions

inclusive, three internodes were at the same time revolving.

The lower internode, when it ceased revolving, became upright and

rigid; but as the whole shoot was left to grow unsupported, it became

after a time bent into a nearly horizontal position, the uppermost

and growing internodes still revolving at the extremity, but of

course no longer round the old central point of the supporting stick.

From the changed position of the centre of gravity of the extremity,

as it revolved, a slight and slow swaying movement was given to the

long horizontally projecting shoot; and this movement I at first

thought was a spontaneous one. As the shoot grew, it hung down more

and more, whilst the growing and revolving extremity turned itself up

more and more.

With the Hop we have seen that three internodes were at the same time

revolving; and this was the case with most of the plants observed by

me. With all, if in full health, two internodes revolved; so that by

the time the lower one ceased to revolve, the one above was in full

action, with a terminal internode just commencing to move. With Hoya

carnosa, on the other hand, a depending shoot, without any developed

leaves, 32 inches in length, and consisting of seven internodes (a

minute terminal one, an inch in length, being counted), continually,

but slowly, swayed from side to side in a semicircular course, with

the extreme internodes making complete revolutions. This swaying

movement was certainly due to the movement of the lower internodes,

which, however, had not force sufficient to swing the whole shoot

round the central supporting stick. The case of another

Asclepiadaceous plant, viz., Ceropegia Gardnerii, is worth briefly

giving. I allowed the top to grow out almost horizontally to the

length of 31 inches; this now consisted of three long internodes,

terminated by two short ones. The whole revolved in a course opposed

to the sun (the reverse of that of the Hop), at rates between 5 hrs.

15 m. and 6 hrs. 45 m. for each revolution. The extreme tip thus

made a circle of above 5 feet (or 62 inches) in diameter and 16 feet

in circumference, travelling at the rate of 32 or 33 inches per hour.

The weather being hot, the plant was allowed to stand on my study-

table; and it was an interesting spectacle to watch the long shoot

sweeping this grand circle, night and day, in search of some object

round which to twine.

If we take hold of a growing sapling, we can of course bend it to all

sides in succession, so as to make the tip describe a circle, like

that performed by the summit of a spontaneously revolving plant. By

this movement the sapling is not in the least twisted round its own

axis. I mention this because if a black point be painted on the

bark, on the side which is uppermost when the sapling is bent towards

the holder's body, as the circle is described, the black point

gradually turns round and sinks to the lower side, and comes up again

when the circle is completed; and this gives the false appearance of

twisting, which, in the case of spontaneously revolving plants,

deceived me for a time. The appearance is the more deceitful because

the axes of nearly all twining-plants are really twisted; and they

are twisted in the same direction with the spontaneous revolving

movement. To give an instance, the internode of the Hop of which the

history has been recorded, was at first, as could be seen by the

ridges on its surface, not in the least twisted; but when, after the

37th revolution, it had grown 9 inches long, and its revolving

movement had ceased, it had become twisted three times round its own

axis, in the line of the course of the sun; on the other hand, the

common Convolvulus, which revolves in an opposite course to the Hop,

becomes twisted in an opposite direction.

Hence it is not surprising that Hugo von Mohl (p. 105, 108, &c.)

thought that the twisting of the axis caused the revolving movement;

but it is not possible that the twisting of the axis of the Hop three

times should have caused thirty-seven revolutions. Moreover, the

revolving movement commenced in the young internode before any

twisting of its axis could be detected. The internodes of a young

Siphomeris and Lecontea revolved during several days, but became

twisted only once round their own axes. The best evidence, however,

that the twisting does not cause the revolving movement is afforded

by many leaf-climbing and tendril-bearing plants (as Pisum sativum,

Echinocystis lobata, Bignonia capreolata, Eccremocarpus scaber, and

with the leaf-climbers, Solanum jasminoides and various species of

Clematis), of which the internodes are not twisted, but which, as we

shall hereafter see, regularly perform revolving movements like those

of true twining-plants. Moreover, according to Palm (pp. 30, 95) and

Mohl (p. 149), and Leon, {5} internodes may occasionally, and even

not very rarely, be found which are twisted in an opposite direction

to the other internodes on the same plant, and to the course of their

revolutions; and this, according to Leon (p. 356), is the case with

all the internodes of a certain variety of Phaseolus multiflorus.

Internodes which have become twisted round their own axes, if they

have not ceased to revolve, are still capable of twining round a

support, as I have several times observed.

Mohl has remarked (p. 111) that when a stem twines round a smooth

cylindrical stick, it does not become twisted. {6} Accordingly I

allowed kidney-beans to run up stretched string, and up smooth rods

of iron and glass, one-third of an inch in diameter, and they became

twisted only in that degree which follows as a mechanical necessity

from the spiral winding. The stems, on the other hand, which had

ascended ordinary rough sticks were all more or less and generally

much twisted. The influence of the roughness of the support in

causing axial twisting was well seen in the stems which had twined up

the glass rods; for these rods were fixed into split sticks below,

and were secured above to cross sticks, and the stems in passing

these places became much twisted. As soon as the stems which had

ascended the iron rods reached the summit and became free, they also

became twisted; and this apparently occurred more quickly during

windy than during calm weather. Several other facts could be given,

showing that the axial twisting stands in some relation to

inequalities in the support, and likewise to the shoot revolving

freely without any support. Many plants, which are not twiners,

become in some degree twisted round their own axes; {7} but this

occurs so much more generally and strongly with twining-plants than

with other plants, that there must be some connexion between the

capacity for twining and axial twisting. The stem probably gains

rigidity by being twisted (on the same principle that a much twisted

rope is stiffer than a slackly twisted one), and is thus indirectly

benefited so as to be enabled to pass over inequalities in its spiral

ascent, and to carry its own weight when allowed to revolve freely.

{8}

I have alluded to the twisting which necessarily follows on

mechanical principles from the spiral ascent of a stem, namely, one

twist for each spire completed. This was well shown by painting

straight lines on living stems, and then allowing them to twine; but,

as I shall have to recur to this subject under Tendrils, it may be

here passed over.

The revolving movement of a twining plant has been compared with that

of the tip of a sapling, moved round and round by the hand held some

way down the stem; but there is one important difference. The upper

part of the sapling when thus moved remains straight; but with

twining plants every part of the revolving shoot has its own separate

and independent movement. This is easily proved; for when the lower

half or two-thirds of a long revolving shoot is tied to a stick, the

upper free part continues steadily revolving. Even if the whole

shoot, except an inch or two of the extremity, be tied up, this part,

as I have seen in the case of the Hop, Ceropegia, Convolvulus, &c.,

goes on revolving, but much more slowly; for the internodes, until

they have grown to some little length, always move slowly. If we

look to the one, two, or several internodes of a revolving shoot,

they will be all seen to be more or less bowed, either during the

whole or during a large part of each revolution. Now if a coloured

streak be painted (this was done with a large number of twining

plants) along, we will say, the convex surface, the streak will after

a time (depending on the rate of revolution) be found to be running

laterally along one side of the bow, then along the concave side,

then laterally on the opposite side, and, lastly, again on the

originally convex surface. This clearly proves that during the

revolving movement the internodes become bowed in every direction.

The movement is, in fact, a continuous self-bowing of the whole

shoot, successively directed to all points of the compass; and has

been well designated by Sachs as a revolving nutation.

As this movement is rather difficult to understand, it will be well

to give an illustration. Take a sapling and bend it to the south,

and paint a black line on the convex surface; let the sapling spring

up and bend it to the east, and the black line will be seen to run

along the lateral face fronting the north; bend it to the north, the

black line will be on the concave surface; bend it to the west, the

line will again be on the lateral face; and when again bent to the

south, the line will be on the original convex surface. Now, instead

of bending the sapling, let us suppose that the cells along its

northern surface from the base to the tip were to grow much more

rapidly than on the three other sides, the whole shoot would then

necessarily be bowed to the south; and let the longitudinal growing

surface creep round the shoot, deserting by slow degrees the northern

side and encroaching on the western side, and so round by the south,

by the east, again to the north. In this case the shoot would remain

always bowed with the painted line appearing on the several above

specified surfaces, and with the point of the shoot successively

directed to each point of the compass. In fact, we should have the

exact kind of movement performed by the revolving shoots of twining

plants. {9}

It must not be supposed that the revolving movement is as regular as

that given in the above illustration; in very many cases the tip

describes an ellipse, even a very narrow ellipse. To recur once

again to our illustration, if we suppose only the northern and

southern surfaces of the sapling alternately to grow rapidly, the

summit would describe a simple arc; if the growth first travelled a

very little to the western face, and during the return a very little

to the eastern face, a narrow ellipse would be described; and the

sapling would be straight as it passed to and fro through the

intermediate space; and a complete straightening of the shoot may

often be observed in revolving plants. The movement is frequently

such that three of the sides of the shoot seem to be growing in due

order more rapidly than the remaining side; so that a semi-circle

instead of a circle is described, the shoot becoming straight and

upright during half of its course.

When a revolving shoot consists of several internodes, the lower ones

bend together at the same rate, but one or two of the terminal ones

bend at a slower rate; hence, though at times all the internodes are

in the same direction, at other times the shoot is rendered slightly

serpentine. The rate of revolution of the whole shoot, if judged by

the movement of the extreme tip, is thus at times accelerated or

retarded. One other point must be noticed. Authors have observed

that the end of the shoot in many twining plants is completely

hooked; this is very general, for instance, with the Asclepiadaceae.

The hooked tip, in all the cases observed by me, viz, in Ceropegia,

Sphaerostemma, Clerodendron, Wistaria, Stephania, Akebia, and

Siphomeris, has exactly the same kind of movement as the other

internodes; for a line painted on the convex surface first becomes

lateral and then concave; but, owing to the youth of these terminal

internodes, the reversal of the hook is a slower process than that of

the revolving movement. {10} This strongly marked tendency in the

young, terminal and flexible internodes, to bend in a greater degree

or more abruptly than the other internodes, is of service to the

plant; for not only does the hook thus formed sometimes serve to

catch a support, but (and this seems to be much more important) it

causes the extremity of the shoot to embrace the support much more

closely than it could otherwise have done, and thus aids in

preventing the stem from being blown away during windy weather, as I

have many times observed. In Lonicera brachypoda the hook only

straightens itself periodically, and never becomes reversed. I will

not assert that the tips of all twining plants when hooked, either

reverse themselves or become periodically straight, in the manner

just described; for the hooked form may in some cases be permanent,

and be due to the manner of growth of the species, as with the tips

of the shoots of the common vine, and more plainly with those of

Cissus discolor--plants which are not spiral twiners.

The first purpose of the spontaneous revolving movement, or, more

strictly speaking, of the continuous bowing movement directed

successively to all points of the compass, is, as Mohl has remarked,

to favour the shoot finding a support. This is admirably effected by

the revolutions carried on night and day, a wider and wider circle

being swept as the shoot increases in length. This movement likewise

explains how the plants twine; for when a revolving shoot meets with

a support, its motion is necessarily arrested at the point of

contact, but the free projecting part goes on revolving. As this

continues, higher and higher points are brought into contact with the

support and are arrested; and so onwards to the extremity; and thus

the shoot winds round its support. When the shoot follows the sun in

its revolving course, it winds round the support from right to left,

the support being supposed to stand in front of the beholder; when

the shoot revolves in an opposite direction, the line of winding is

reversed. As each internode loses from age its power of revolving,

it likewise loses its power of spirally twining. If a man swings a

rope round his head, and the end hits a stick, it will coil round the

stick according to the direction of the swinging movement; so it is

with a twining plant, a line of growth travelling round the free part

of the shoot causing it to bend towards the opposite side, and this

replaces the momentum of the free end of the rope.

All the authors, except Palm and Mohl, who have discussed the spiral

twining of plants, maintain that such plants have a natural tendency

to grow spirally. Mohl believes (p. 112) that twining stems have a

dull kind of irritability, so that they bend towards any object which

they touch; but this is denied by Palm. Even before reading Mohl's

interesting treatise, this view seemed to me so probable that I

tested it in every way that I could, but always with a negative

result. I rubbed many shoots much harder than is necessary to excite

movement in any tendril or in the foot-stalk of any leaf climber, but

without any effect. I then tied a light forked twig to a shoot of a

Hop, a Ceropegia, Sphaerostemma, and Adhatoda, so that the fork

pressed on one side alone of the shoot and revolved with it; I

purposely selected some very slow revolvers, as it seemed most likely

that these would profit most from possessing irritability; but in no

case was any effect produced. {11} Moreover, when a shoot winds

round a support, the winding movement is always slower, as we shall

immediately see, than whilst it revolves freely and touches nothing.

Hence I conclude that twining stems are not irritable; and indeed it

is not probable that they should be so, as nature always economizes

her means, and irritability would have been superfluous.

Nevertheless I do not wish to assert that they are never irritable;

for the growing axis of the leaf-climbing, but not spirally twining,

Lophospermum scandens is, certainly irritable; but this case gives me

confidence that ordinary twiners do not possess any such quality, for

directly after putting a stick to the Lophopermum, I saw that it

behaved differently from a true twiner or any other leaf-climber.

{12}

The belief that twiners have a natural tendency to grow spirally,

probably arose from their assuming a spiral form when wound round a

support, and from the extremity, even whilst remaining free,

sometimes assuming this form. The free internodes of vigorously

growing plants, when they cease to revolve, become straight, and show

no tendency to be spiral; but when a shoot has nearly ceased to grow,

or when the plant is unhealthy, the extremity does occasionally

become spiral. I have seen this in a remarkable manner with the ends

of the shoots of the Stauntonia and of the allied Akebia, which

became wound up into a close spire, just like a tendril; and this was

apt to occur after some small, ill-formed leaves had perished. The

explanation, I believe, is, that in such cases the lower parts of the

terminal internodes very gradually and successively lose their power

of movement, whilst the portions just above move onwards and in their

turn become motionless; and this ends in forming an irregular spire.

When a revolving shoot strikes a stick, it winds round it rather more

slowly than it revolves. For instance, a shoot of the Ceropegia,

revolved in 6 hrs., but took 9 hrs. 30 m. to make one complete spire

round a stick; Aristolochia gigas revolved in about 5 hrs., but took

9 hrs. 15 m. to complete its spire. This, I presume, is due to the

continued disturbance of the impelling force by the arrestment of the

movement at successive points; and we shall hereafter see that even

shaking a plant retards the revolving movement. The terminal

internodes of a long, much-inclined, revolving shoot of the

Ceropegia, after they had wound round a stick, always slipped up it,

so as to render the spire more open than it was at first; and this

was probably in part due to the force which caused the revolutions,

being now almost freed from the constraint of gravity and allowed to

act freely. With the Wistaria, on the other hand, a long horizontal

shoot wound itself at first into a very close spire, which remained

unchanged; but subsequently, as the shoot twined spirally up its

support, it made a much more open spire. With all the many plants

which were allowed freely to ascend a support, the terminal

internodes made at first a close spire; and this, during windy

weather, served to keep the shoots in close contact with their

support; but as the penultimate internodes grew in length, they

pushed themselves up for a considerable space (ascertained by

coloured marks on the shoot and on the support) round the stick, and

the spire became more open. {13}

It follows from this latter fact that the position occupied by each

leaf with respect to the support depends on the growth of the

internodes after they have become spirally wound round it. I mention

this on account of an observation by Palm (p. 34), who states that

the opposite leaves of the Hop always stand in a row, exactly over

one another, on the same side of the supporting stick, whatever its

thickness may be. My sons visited a hop-field for me, and reported

that though they generally found the points of insertion of the

leaves standing over each other for a space of two or three feet in

height, yet this never occurred up the whole length of the pole; the

points of insertion forming, as might have been expected, an

irregular spire. Any irregularity in the pole entirely destroyed the

regularity of position of the leaves. From casual inspection, it

appeared to me that the opposite leaves of Thunbergia alata were

arranged in lines up the sticks round which they had twined;

accordingly, I raised a dozen plants, and gave them sticks of various

thicknesses, as well as string, to twine round; and in this case one

alone out of the dozen had its leaves arranged in a perpendicular

line: I conclude, therefore, Palm's statement is not quite accurate.

The leaves of different twining-plants are arranged on the stem

(before it has twined) alternately, or oppositely, or in a spire. In

the latter case the line of insertion of the leaves and the course of

the revolutions coincide. This fact has been well shown by

Dutrochet, {14} who found different individuals of Solanum dulcamara

twining in opposite directions, and these had their leaves in each

case spirally arranged in the same direction. A dense whorl of many

leaves would apparently be incommodious for a twining plant, and some

authors assert that none have their leaves thus arranged; but a

twining Siphomeris has whorls of three leaves.

If a stick which has arrested a revolving shoot, but has not as yet

been encircled, be suddenly taken away, the shoot generally springs

forward, showing that it was pressing with some force against the

stick. After a shoot has wound round a stick, if this be withdrawn,

it retains for a time its spiral form; it then straightens itself,

and again commences to revolve. The long, much-inclined shoot of the

Ceropegia previously alluded to offered some curious peculiarities.

The lower and older internodes, which continued to revolve, were

incapable, on repeated trials, of twining round a thin stick; showing

that, although the power of movement was retained, this was not

sufficient to enable the plant to twine. I then moved the stick to a

greater distance, so that it was struck by a point 2.5 inches from

the extremity of the penultimate internode; and it was then neatly

encircled by this part of the penultimate and by the ultimate

internode. After leaving the spirally wound shoot for eleven hours,

I quietly withdrew the stick, and in the course of the day the curled

portion straightened itself and recommenced revolving; but the lower

and not curled portion of the penultimate internode did not move, a

sort of hinge separating the moving and the motionless part of the

same internode. After a few days, however, I found that this lower

part had likewise recovered its revolving power. These several facts

show that the power of movement is not immediately lost in the

arrested portion of a revolving shoot; and that after being

temporarily lost it can be recovered. When a shoot has remained for

a considerable time round a support, it permanently retains its

spiral form even when the support is removed.

When a tall stick was placed so as to arrest the lower and rigid

internodes of the Ceropegia, at the distance at first of 15 and then

of 21 inches from the centre of revolution, the straight shoot slowly

and gradually slid up the stick, so as to become more and more highly

inclined, but did not pass over the summit. Then, after an interval

sufficient to have allowed of a semi-revolution, the shoot suddenly

bounded from the stick and fell over to the opposite side or point of

the compass, and reassumed its previous slight inclination. It now

recommenced revolving in its usual course, so that after a semi-

revolution it again came into contact with the stick, again slid up

it, and again bounded from it and fell over to the opposite side.

This movement of the shoot had a very odd appearance, as if it were

disgusted with its failure but was resolved to try again. We shall,

I think, understand this movement by considering the former

illustration of the sapling, in which the growing surface was

supposed to creep round from the northern by the western to the

southern face; and thence back again by the eastern to the northern

face, successively bowing the sapling in all directions. Now with

the Ceropegia, the stick being placed to the south of the shoot and

in contact with it, as soon as the circulatory growth reached the

western surface, no effect would be produced, except that the shoot

would be pressed firmly against the stick. But as soon as growth on

the southern surface began, the shoot would be slowly dragged with a

sliding movement up the stick; and then, as soon as the eastern

growth commenced, the shoot would be drawn from the stick, and its

weight coinciding with the effects of the changed surface of growth,

would cause it suddenly to fall to the opposite side, reassuming its

previous slight inclination; and the ordinary revolving movement

would then go on as before. I have described this curious case with

some care, because it first led me to understand the order in which,

as I then thought, the surfaces contracted; but in which, as we now

know from Sachs and II. de Vries, they grow for a time rapidly, thus

causing the shoot to bow towards the opposite side.

The view just given further explains, as I believe, a fact observed

by Mohl (p. 135), namely, that a revolving shoot, though it will

twine round an object as thin as a thread, cannot do so round a thick

support. I placed some long revolving shoots of a Wistaria close to

a post between 5 and 6 inches in diameter, but, though aided by me in

many ways, they could not wind round it. This apparently was due to

the flexure of the shoot, whilst winding round an object so gently

curved as this post, not being sufficient to hold the shoot to its

place when the growing surface crept round to the opposite surface of

the shoot; so that it was withdrawn at each revolution from its

support.

When a free shoot has grown far beyond its support, it sinks

downwards from its weight, as already explained in the case of the

Hop, with the revolving extremity turned upwards. If the support be

not lofty, the shoot falls to the ground, and resting there, the

extremity rises up. Sometimes several shoots, when flexible, twine

together into a cable, and thus support one another. Single thin

depending shoots, such as those of the Sollya Drummondii, will turn

abruptly backwards and wind up on themselves. The greater number of

the depending shoots, however, of one twining plant, the Hibbertia

dentata, showed but little tendency to turn upwards. In other cases,

as with the Cryptostegia grandiflora, several internodes which were

at first flexible and revolved, if they did not succeed in twining

round a support, become quite rigid, and supporting themselves

upright, carried on their summits the younger revolving internodes.

Here will be a convenient place to give a Table showing the direction

and rate of movement of several twining plants, with a few appended

remarks. These plants are arranged according to Lindley's 'Vegetable

Kingdom' of 1853; and they have been selected from all parts of the

series so as to show that all kinds behave in a nearly uniform

manner. {15}

The Rate of Revolution of various Twining Plants.

(ACOTYLEDONS.)

Lygodium scandens (Polypodiaceae) moves against the sun.

H. M.

June 18, 1st circle was made in 6 0

18, 2nd 6 15 (late in evening)

19, 3rd 5 32 (very hot day)

19, 4th 5 0 (very hot day)

20, 5th 6 0

Lygodium articulatum moves against the sun.

H. M.

July 19, 1st circle was made in 16 30 (shoot very young)

20, 2nd 15 0

21, 3rd 8 0

22, 4th 10 30

(MONOCOTYLEDONS.)

Ruscus androgynus (Liliaceae), placed in the hot-house, moves against

the sun.

H. M.

May 24, 1st circle was made in 6 14 (shoot very young)

25, 2nd 2 21

25, 3rd 3 37

25, 4th 3 22

26, 5th 2 50

27, 6th 3 52

27, 7th 4 11

Asparagus (unnamed species from Kew) (Liliaceae) moves against the

sun, placed in hothouse.

H. M.

Dec. 26, 1st circle was made in 5 0

27, 2nd 5 40

Tamus communis (Dioscoreaceae). A young shoot from a tuber in a pot

placed in the greenhouse: follows the sun.

H. M.

July, 7, 1st circle was made in 3 10

7, 2nd 2 38

8, 3rd 3 5

8, 4th 2 56

8, 5th 2 30

8, 6th 2 30

Lapagerea rosea (Philesiaceae), in greenhouse, follows the sun.

H. M.

March 9, 1st circle was made in 26 15 (shoot young)

10, semicircle 8 15

11, 2nd circle 11 0

12, 3rd 15 30

13, 4th 14 15

16, 5th 8 40 when placed in the

hothouse; but the next day the shoot remained stationary.

Roxburghia viridiflora (Roxburghiaceae) moves against the sun; it

completed a circle in about 24 hours.

(DICOTYLEDONS.)

Humulus Lupulus (Urticaceae) follows the sun. The plant was kept in

a room during warm weather.

H. M.

April 9, 2 circles were made in 4 16

Aug. 13, 3rd circle was 2 0

14, 4th 2 20

14, 5th 2 16

14, 6th 2 2

14, 7th 2 0

14, 8th 2 4

With the Hop a semicircle was performed, in travelling from the

light, in 1 hr. 33 m.; in travelling to the light, in 1 hr. 13 m.;

difference of rate, 20 m.

Akebia quinata (Lardizabalaceae), placed in hothouse, moves against

the sun.

H. M.

March 17, 1st circle was made in 4 0 (shoot young)

18, 2nd 1 40

18, 3rd 1 30

19, 4th 1 45

Stauntonia latifolia (Lardizabalaceae), placed in hothouse, moves

against the sun.

H. M.

March 28, 1st circle was made in 3 30

29, 2nd 3 45

Sphaerostemma marmoratum (Schizandraceae) follows the sun.

H. M.

August 5th, 1st circle was made in about 24 0

5th, 2nd circle was made in 18 30

Stephania rotunda (Menispermaceae) moves against the sun

H. M.

May 27, 1st circle was made in 5 5

30, 2nd 7 6

June 2, 3rd 5 15

3, 4th 6 28

Thryallis brachystachys (Malpighiaceae) moves against the sun: one

shoot made a circle in 12 hrs., and another in 10 hrs. 30 m.; but the

next day, which was much colder, the first shoot took 10 hrs. to

perform only a semicircle.

Hibbertia dentata (Dilleniaceae), placed in the hothouse, followed

the sun, and made (May 18th) a circle in 7 hrs. 20 m.; on the 19th,

reversed its course, and moved against the sun, and made a circle in

7 hrs.; on the 20th, moved against the sun one-third of a circle, and

then stood still; on the 26th, followed the sun for two-thirds of a

circle, and then returned to its starting-point, taking for this

double course 11 hrs. 46 m.

Sollya Drummondii (Pittosporaceae) moves against the sun kept in

greenhouse.

H. M.

April 4, 1st circle was made in 4 25

5, 2nd 8 0 (very cold day)

6, 3rd 6 25

7, 4th 7 5

Polygonum dumetorum (Polygonaceae). This case is taken from

Dutrochet (p. 299), as I observed, no allied plant: follows the

sun. Three shoots, cut off a plant, and placed in water made circles

in 3 hrs. 10 m., 5 hrs. 20 m., and 7 hrs. 15 m.

Wistaria Chinensis (Leguminosae), in greenhouse, moves against the

sun.

H. M.

May 13, 1st circle was made in 3 5

13, 2nd 3 20

16, 3rd 2 5

24, 4th 3 21

25, 5th 2 37

25, 6th 2 35

Phaseolus vulgaris (Leguminosae), in greenhouse, moves against the

sun.

H. M.

May, 1st circle was made in 2 0

2nd 1 55

3rd 1 55

Dipladenia urophylla (Apocynaceae) moves against the sun.

H. M.

April 18, 1st circle was made in 8 0

19, 2nd 9 15

30, 3rd 9 40

Dipladenia crassinoda moves against the sun.

H. M.

May 16, 1st circle was made in 9 5

July 20, 2nd 8 0

21, 3rd 8 5

Ceropegia Gardnerii (Asclepiadaceae) moves against the sun.

H. M.

Shoot very young, 2 inches }

in length } 1st circle was performed in 7 55

Shoot still young 2nd 7 0

Long shoot 3rd 6 33

Long shoot 4th 5 15

Long shoot 5th 6 45

Stephanotis floribunda (Asclepiadaceae) moves against the sun and

made a circle in 6 hrs. 40 m., a second circle in about 9 hrs.

Hoya carnosa (Asclepiadaceae) made several circles in from 16 hrs. to

22 hrs. or 24 hrs.

Ipomaea purpurea (Convolvulaceae) moves against the sun. Plant

placed in room with lateral light.

{Semicircle, from the light in

1st circle was made in 2 hrs. 42 m. { 1 hr. 14 m., to the light

{ 1 hr. 28 m.: difference 14 m.

{Semicircle, from the light in

2nd circle was made in 2 hrs. 47 m. { 1 hr. 17 m., to the light 1 hr.

{ 30 m.: difference 13 m.

Ipomaea jucunda (Convolvulaceae) moves against the sun, placed in my

study, with windows facing the north-east. Weather hot.

{Semicircle, from the light in

1st circle was made in 5 hrs. 30 m. { 4 hrs. 30 m., to the light 1

hr.

{ 0 m.: difference 3 hrs. 30 m.

2nd circle was made in 5 hrs. {Semicircle, from the light in

20 m. (Late in afternoon: { 3 hrs. 50 m., to the light 1

hr.

circle completed at 6 hrs. 40 m. { 30 m.: difference 2 hrs. 20 m.

P.M.)

We have here a remarkable instance of the power of light in retarding

and hastening the revolving movement. (See ERRATA.)

Convolvulus sepium (large-flowered cultivated var.) moves against the

sun. Two circles, were made each in 1 hr. 42 m.: difference in

semicircle from and to the light 14 m.

Rivea tiliaefolia (Convolvulaceae) moves against the sun, made four

revolutions in 9 hrs.; so that, on an average, each was performed in

2 hrs. 15 m.

Plumbago rosea (Plumbaginaceae) follows the sun. The shoot did not

begin to revolve until nearly a yard in height; it then made a fine

circle in 10 hrs. 45 m. During the next few days it continued to

move, but irregularly. On August 15th the shoot followed, during a

period of 10 hrs. 40 m., a long and deeply zigzag course and then

made a broad ellipse. The figure apparently represented three

ellipses, each of which averaged 3 hrs. 38 m. for its completion.

Jasminum pauciflorum, Bentham (Jasminaceae), moves against the sun.

A circle was made in 7 hrs. 15 m., and a second rather more quickly.

Clerodendrum Thomsonii (Verbenaceae) follows the sun.

H. M.

April 12, 1st circle was made in 5 45 (shoot very young)

14, 2nd 3 30

{(directly after the

18, a semicircle 5 0 { plant was shaken

{ on being moved)

19, 3rd circle 3 0

20, 4th 4 20

Tecoma jasminoides (Bignoniaceae) moves against the sun.

H. M.

March 17, 1st circle was made in 6 30

19, 2nd 7 0

22, 3rd 8 30 (very cold day)

24, 4th 6 45

Thunbergia alata (Acanthaceae) moves against sun.

H. M.

April 14, 1st circle was made in 3 20

18, 2nd 2 50

18, 3rd 2 55

18, 4th 3 55 (late in afternoon)

Adhadota cydonaefolia (Acanthaceae) follows the sun. A young shoot

made a semicircle in 24 hrs.; subsequently it made a circle in

between 40 hrs. and 48 hrs. Another shoot, however, made a circle in

26 hrs. 30 m.

Mikania scandens (Compositae) moves against the sun.

H. M.

March 14, 1st circle was made in 3 10

15, 2nd 3 0

16, 3rd 3 0

17, 4th 3 33

April 7, 5th 2 50

7, 6th 2 40 {This circle was

made

{ after a copious

water-

{ ing with cold

water at

{ 47 degrees Fahr.

Combretum argenteum (Combretaceae) moves against the sun. Kept in

hothouse.

H. M.

{Early in morning,

when

Jan. 24, 1st circle was made in 2 55 { the temperature of

the

{ house had fallen a

{ little.

24, 2 circles each at an }

average of } 2 20

25, 4th circle was made in 2 25

Combretum purpureum revolves not quite so quickly as C. argenteum.

Loasa aurantiaca (Loasaceae). Revolutions variable in their course:

a plant which moved against the sun.

H. M.

June 20, 1st circle was made in 2 37

20, 2nd 2 13

20, 3rd 4 0

21, 4th 2 35

22, 5th 3 26

23, 6th 3 5

Another plant which followed the sun in its revolutions.

H. M.

July 11, 1st circle was made in 1 51 }

11, 2nd 1 46 } Very hot day.

11, 3rd 1 41 }

11, 4th 1 48 }

12, 5th 2 35 }

Scyphanthus elegans (Loasaceae) follows the sun.

H. M.

June 13, 1st circle was made in 1 45

13, 2nd 1 17

14, 3rd 1 36

14, 4th 1 59

14, 5th 2 3

Siphomeris or Lecontea (unnamed sp.) (Cinchonaceae) follows the sun.

H. M.

{(shoot extremely

May 25, semicircle was made in 10 27 { young)

26, 1st circle 10 15 (shoot still young)

30, 2nd 8 55

June 2, 3rd 8 11

6, 4th 6 8

{ Taken from the

8, 5th 7 20 { hothouse, and

9, 6th 8 36 { placed in a room

{ in my house.

Manettia bicolor (Cinchonaceae), young plant, follows the sun.

H. M.

July 7, 1st circle was made in 6 18

8, 2nd 6 53

9, 3rd 6 30

Lonicera brachypoda (Caprifoliaceae) follows the sun, kept in a warm

room in the house.

H. M.

April, 1st circle was made in 9 10 (about)

{(a distinct shoot,

very

April, 2nd circle was made in 12 20 { young, on same

plant)

3rd 7 30

{In this latter

circle,

{ the semicircle from

{ the light took 5

hrs.

4th 8 0 { 23 m., and to the

{ light 2 hrs. 37

min.:

{ difference 2 hrs

46m.

Aristolochia gigas (Aristolochiaceae) moves against the sun.

H. M.

July 22, 1st circle was made in 8 0 (rather young shoot)

23, 2nd 7 15

24, 3rd 5 0 (about)

In the foregoing Table, which includes twining plants belonging to

widely different orders, we see that the rate at which growth travels

or circulates round the axis (on which the revolving movement

depends), differs much. As long as a plant remains under the same

conditions, the rate is often remarkably uniform, as with the Hop,

Mikania, Phaseolus, &c. The Scyphanthus made one revolution in 1 hr.

17 m., and this is the quickest rate observed by me; but we shall

hereafter see a tendril-bearing Passiflora revolving more rapidly. A

shoot of the Akebia quinata made a revolution in 1 hr. 30 m., and

three revolutions at the average rate of 1 hr. 38 m.; a Convolvulus

made two revolutions at the average of 1 hr. 42 m., and Phaseolus

vulgaris three at the average of 1 hr. 57 m. On the other hand, some

plants take 24 hrs. for a single revolution, and the Adhadota

sometimes required 48 hrs.; yet this latter plant is an efficient

twiner. Species of the same genus move at different rates. The rate

does not seem governed by the thickness of the shoots: those of the

Sollya are as thin and flexible as string, but move more slowly than

the thick and fleshy shoots of the Ruscus, which seem little fitted

for movement of any kind. The shoots of the Wistaria, which become

woody, move faster than those of the herbaceous Ipomoea or

Thunbergia.

We know that the internodes, whilst still very young, do not acquire

their proper rate of movement; hence the several shoots on the same

plant may sometimes be seen revolving at different rates. The two or

three, or even more, internodes which are first formed above the

cotyledons, or above the root-stock of a perennial plant, do not

move; they can support themselves, and nothing superfluous is

granted.

A greater number of twiners revolve in a course opposed to that of

the sun, or to the hands of a watch, than in the reversed course,

and, consequently, the majority, as is well known, ascend their

supports from left to right. Occasionally, though rarely, plants of

the same order twine in opposite directions, of which Mohl (p. 125)

gives a case in the Leguminosae, and we have in the table another in

the Acanthaceae. I have seen no instance of two species of the same

genus twining in opposite directions, and such cases must be rare;

but Fritz Muller {16} states that although Mikania scandens twines,

as I have described, from left to right, another species in South

Brazil twines in an opposite direction. It would have been an

anomalous circumstance if no such cases had occurred, for different

individuals of the same species, namely, of Solanum dulcamara

(Dutrochet, tom. xix. p. 299), revolve and twine in two directions:

this plant, however; is a most feeble twiner. Loasa aurantiaca

(Leon, p. 351) offers a much more curious case: I raised seventeen

plants: of these eight revolved in opposition to the sun and

ascended from left to right; five followed the sun and ascended from

right to left; and four revolved and twined first in one direction,

and then reversed their course, {17} the petioles of the opposite

leaves affording a point d'appui for the reversal of the spire. One

of these four plants made seven spiral turns from right to left, and

five turns from left to right. Another plant in the same family, the

Scyphanthus elegans, habitually twines in this same manner. I raised

many plants of it, and the stems of all took one turn, or

occasionally two or even three turns in one direction, and then,

ascending for a short space straight, reversed their course and took

one or two turns in an opposite direction. The reversal of the

curvature occurred at any point in the stem, even in the middle of an

internode. Had I not seen this case, I should have thought its

occurrence most improbable. It would be hardly possible with any

plant which ascended above a few feet in height, or which lived in an

exposed situation; for the stem could be pulled away easily from its

support, with but little unwinding; nor could it have adhered at all,

had not the internodes soon become moderately rigid. With leaf-

climbers, as we shall soon see, analogous cases frequently occur; but

these present no difficulty, as the stem is secured by the clasping

petioles.

In the many other revolving and twining plants observed by me, I

never but twice saw the movement reversed; once, and only for a short

space, in Ipomoea jucunda; but frequently with Hibbertia dentata.

This plant at first perplexed me much, for I continually observed its

long and flexible shoots, evidently well fitted for twining, make a

whole, or half, or quarter circle in one direction and then in an

opposite direction; consequently, when I placed the shoots near thin

or thick sticks, or perpendicularly stretched string, they seemed as

if constantly trying to ascend, but always failed. I then surrounded

the plant with a mass of branched twigs; the shoots ascended, and

passed through them, but several came out laterally, and their

depending extremities seldom turned upwards as is usual with twining

plants. Finally, I surrounded a second plant with many thin upright

sticks, and placed it near the first one with twigs; and now both had

got what they liked, for they twined up the parallel sticks,

sometimes winding round one and sometimes round several; and the

shoots travelled laterally from one to the other pot; but as the

plants grew older, some of the shoots twined regularly up thin

upright sticks. Though the revolving movement was sometimes in one

direction and sometimes in the other, the twining was invariably from

left to right; {18} so that the more potent or persistent movement of

revolution must have been in opposition to the course of the sun. It

would appear that this Hibbertia is adapted both to ascend by

twining, and to ramble laterally through the thick Australian scrub.

I have described the above case in some detail, because, as far as I

have seen, it is rare to find any special adaptations with twining

plants, in which respect they differ much from the more highly

organized tendril-bearers. The Solanum dulcamara, as we shall

presently see, can twine only round stems which are both thin and

flexible. Most twining plants are adapted to ascend supports of

moderate though of different thicknesses. Our English twiners, as

far as I have seen, never twine round trees, excepting the

honeysuckle (Lonicera periclymenum), which I have observed twining up

a young beech-tree nearly 4.5 inches in diameter. Mohl (p. 134)

found that the Phaseolus multiflorus and Ipomoea purpurea could not,

when placed in a room with the light entering on one side, twine

round sticks between 3 and 4 inches in diameter; for this interfered,

in a manner presently to be explained, with the revolving movement.

In the open air, however, the Phaseolus twined round a support of the

above thickness, but failed in twining round one 9 inches in

diameter. Nevertheless, some twiners of the warmer temperate regions

can manage this latter degree of thickness; for I hear from Dr.

Hooker that at Kew the Ruscus androgynus has ascended a column 9

inches in diameter; and although a Wistaria grown by me in a small

pot tried in vain for weeks to get round a post between 5 and 6

inches in thickness, yet at Kew a plant ascended a trunk above 6

inches in diameter. The tropical twiners, on the other hand, can

ascend thicker trees; I hear from Drs. Thomson and Hooker that this

is the case with the Butea parviflora, one of the Menispermaceae, and

with some Dalbergias and other Leguminosae. {19} This power would be

necessary for any species which had to ascend by twining the large

trees of a tropical forest; otherwise they would hardly ever be able

to reach the light. In our temperate countries it would be injurious

to the twining plants which die down every year if they were enabled

to twine round trunks of trees, for they could not grow tall enough

in a single season to reach the summit and gain the light.

By what means certain twining plants are adapted to ascend only thin

stems, whilst others can twine round thicker ones, I do not know. It

appeared to me probable that twining plants with very long revolving

shoots would be able to ascend thick supports; accordingly I placed

Ceropegia Gardnerii near a post 6 inches in diameter, but the shoots

entirely failed to wind round it; their great length and power of

movement merely aid them in finding a distant stem round which to

twine. The Sphaerostemma marmoratum is a vigorous tropical twiner;

and as it is a very slow revolver, I thought that this latter

circumstance might help it in ascending a thick support; but though

it was able to wind round a 6-inch post, it could do this only on the

same level or plane, and did not form a spire and thus ascend.

As ferns differ so much in structure from phanerogamic plants, it may

be worth while here to show that twining ferns do not differ in their

habits from other twining plants. In Lygodium articulatum the two

internodes of the stem (properly the rachis) which are first formed

above the root-stock do not move; the third from the ground revolves,

but at first very slowly. This species is a slow revolver: but L.

scandens made five revolutions, each at the average rate of 5 hrs. 45

m.; and this represents fairly well the usual rate, taking quick and

slow movers, amongst phanerogamic plants. The rate was accelerated

by increased temperature. At each stage of growth only the two upper

internodes revolved. A line painted along the convex surface of a

revolving internode becomes first lateral, then concave, then lateral

and ultimately again convex. Neither the internodes nor the petioles

are irritable when rubbed. The movement is in the usual direction,

namely, in opposition to the course of the sun; and when the stem

twines round a thin stick, it becomes twisted on its own axis in the

same direction. After the young internodes have twined round a

stick, their continued growth causes them to slip a little upwards.

If the stick be soon removed, they straighten themselves, and

recommence revolving. The extremities of the depending shoots turn

upwards, and twine on themselves. In all these respects we have

complete identity with twining phanerogamic plants; and the above

enumeration may serve as a summary of the leading characteristics of

all twining plants.

The power of revolving depends on the general health and vigour of

the plant, as has been laboriously shown by Palm. But the movement

of each separate internode is so independent of the others, that

cutting off an upper one does not affect the revolutions of a lower

one. When, however, Dutrochet cut off two whole shoots of the Hop,

and placed them in water, the movement was greatly retarded; for one

revolved in 20 hrs. and the other in 23 hrs., whereas they ought to

have revolved in between 2 hrs. and 2 hrs. 30 m. Shoots of the

Kidney-bean, cut off and placed in water, were similarly retarded,

but in a less degree. I have repeatedly observed that carrying a

plant from the greenhouse to my room, or from one part to another of

the greenhouse, always stopped the movement for a time; hence I

conclude that plants in a state of nature and growing in exposed

situations, would not make their revolutions during very stormy

weather. A decrease in temperature always caused a considerable

retardation in the rate of revolution; but Dutrochet (tom. xvii. pp.

994, 996) has given such precise observations on this head with

respect to the common pea that I need say nothing more. When twining

plants are placed near a window in a room, the light in some cases

has a remarkable power (as was likewise observed by Dutrochet, p.

998, with the pea) on the revolving movement, but this differs in

degree with different plants; thus Ipomoea jucunda made a complete

circle in 5 hrs. 30 m.; the semicircle from the light taking 4 hrs.

80 m., and that towards the light only 1 hr. Lonicera brachypoda

revolved, in a reversed direction to the Ipomoea, in 8 hrs.; the

semicircle from the light taking 5 hrs. 23 m., and that to the light

only 2 hrs. 37 m. From the rate of revolution in all the plants

observed by me, being nearly the same during the night and the day, I

infer that the action of the light is confined to retarding one

semicircle and accelerating the other, so as not to modify greatly

the rate of the whole revolution. This action of the light is

remarkable, when we reflect how little the leaves are developed on

the young and thin revolving internodes. It is all the more

remarkable, as botanists believe (Mohl, p. 119) that twining plants

are but little sensitive to the action of light.

I will conclude my account of twining plants by giving a few

miscellaneous and curious cases. With most twining plants all the

branches, however many there may be, go on revolving together; but,

according to Mohl (p. 4), only the lateral branches of Tamus

elephantipes twine, and not the main stem. On the other hand, with a

climbing species of Asparagus, the leading shoot alone, and not the

branches, revolved and twined; but it should be stated that the plant

was not growing vigorously. My plants of Combretum argenteum and C.

purpureum made numerous short healthy shoots; but they showed no

signs of revolving, and I could not conceive how these plants could

be climbers; but at last C. argenteum put forth from the lower part

of one of its main branches a thin shoot, 5 or 6 feet in length,

differing greatly in appearance from the previous shoots, owing to

its leaves being little developed, and this shoot revolved vigorously

and twined. So that this plant produces shoots of two kinds. With

Periploca Graeca (Palm, p. 43) the uppermost shoots alone twine.

Polygonum convolvulus twines only during the middle of the summer

(Palm, p. 43, 94); and plants growing vigorously in the autumn show

no inclination to climb. The majority of Asclepiadaceae are twiners;

but Asclepias nigra only "in fertiliori solo incipit scandere

subvolubili caule" (Willdenow, quoted and confirmed by Palm, p. 41).

Asclepias vincetoxicum does not regularly twine, but occasionally

does so (Palm, p. 42; Mohl, p. 112) when growing under certain

conditions. So it is with two species of Ceropegia, as I hear from

Prof. Harvey, for these plants in their native dry South African

home generally grow erect, from 6 inches to 2 feet in height,--a very

few taller specimens showing some inclination to curve; but when

cultivated near Dublin, they regularly twined up sticks 5 or 6 feet

in height. Most Convolvulaceae are excellent twiners; but in South

Africa Ipomoea argyraeoides almost always grows erect and compact,

from about 12 to 18 inches in height, one specimen alone in Prof.

Harvey's collection showing an evident disposition to twine. On the

other hand, seedlings raised near Dublin twined up sticks above 8

feet in height. These facts are remarkable; for there can hardly be

a doubt that in the dryer provinces of South Africa these plants have

propagated themselves for thousands of generations in an erect

condition; and yet they have retained during this whole period the

innate power of spontaneously revolving and twining, whenever their

shoots become elongated under proper conditions of life. Most of the

species of Phaseolus are twiners; but certain varieties of the P.

multiflorus produce (Leon, p. 681) two kinds of shoots, some upright

and thick, and others thin and twining. I have seen striking

instances of this curious case of variability in "Fulmer's dwarf

forcing-bean," which occasionally produced a single long twining

shoot.

Solanum dulcamara is one of the feeblest and poorest of twiners: it

may often be seen growing as an upright bush, and when growing in the

midst of a thicket merely scrambles up between the branches without

twining; but when, according to Dutrochet (tom. xix. p. 299), it

grows near a thin and flexible support, such as the stem of a nettle,

it twines round it. I placed sticks round several plants, and

vertically stretched strings close to others, and the strings alone

were ascended by twining. The stem twines indifferently to the right

or left. Some others species of Solanum, and of another genus, viz.

Habrothamnus, belonging to the same family, are described in

horticultural works as twining plants, but they seem to possess this

faculty in a very feeble degree. We may suspect that the species of

these two genera have as yet only partially acquired the habit of

twining. On the other hand with Tecoma radicans, a member of a

family abounding with twiners and tendril-bearers, but which climbs,

like the ivy, by the aid of rootlets, we may suspect that a former

habit of twining has been lost, for the stem exhibited slight

irregular movements which could hardly be accounted for by changes in

the action of the light. There is no difficulty in understanding how

a spirally twining plant could graduate into a simple root-climber;

for the young internodes of Bignonia Tweedyana and of Hoya carnosa

revolve and twine, but likewise emit rootlets which adhere to any

fitting surface, so that the loss of twining would be no great

disadvantage and in some respects an advantage to these species, as

they would then ascend their supports in a more direct line. {20}

CHAPTER II.--LEAF-CLIMBERS.

Plants which climb by the aid of spontaneously revolving and

sensitive petioles--Clematis--Tropaeolum--Maurandia, flower-peduncles

moving spontaneously and sensitive to a touch--Rhodochiton--

Lophospermum--internodes sensitive--Solanum, thickening of the

clasped petioles--Fumaria--Adlumia--Plants which climb by the aid of

their produced midribs--Gloriosa--Flagellaria--Nepenthes--Summary on

leaf-climbers.

We now come to our second class of climbing plants, namely, those

which ascend by the aid of irritable or sensitive organs. For

convenience' sake the plants in this class have been grouped under

two sub-divisions, namely, leaf-climbers, or those which retain their

leaves in a functional condition, and tendril-bearers. But these

sub-divisions graduate into each other, as we shall see under

Corydalis and the Gloriosa lily.

It has long been observed that several plants climb by the aid of

their leaves, either by their petioles (foot-stalks) or by their

produced midribs; but beyond this simple fact they have not been

described. Palm and Mohl class these plants with those which bear

tendrils; but as a leaf is generally a defined object, the present

classification, though artificial, has at least some advantages.

Leaf-climbers are, moreover, intermediate in many respects between

twiners and tendril-bearers. Eight species of Clematis and seven of

Tropaeolum were observed, in order to see what amount of difference

in the manner of climbing existed within the same genus; and the

differences are considerable.

CLEMATIS.--C. glandulosa.--The thin upper internodes revolve, moving

against the course of the sun, precisely like those of a true twiner,

at an average rate, judging from three revolutions, of 3 hrs. 48 m.

The leading shoot immediately twined round a stick placed near it;

but, after making an open spire of only one turn and a half, it

ascended for a short space straight, and then reversed its course and

wound two turns in an opposite direction. This was rendered possible

by the straight piece between the opposed spires having become rigid.

The simple, broad, ovate leaves of this tropical species, with their

short thick petioles, seem but ill-fitted for any movement; and

whilst twining up a vertical stick, no use is made of them.

Nevertheless, if the footstalk of a young leaf be rubbed with a thin

twig a few times on any side, it will in the course of a few hours

bend to that side; afterwards becoming straight again. The under

side seemed to be the most sensitive; but the sensitiveness or

irritability is slight compared to that which we shall meet with in

some of the following species; thus, a loop of string, weighing 1.64

grain (106.2 mg.) and hanging for some days on a young footstalk,

produced a scarcely perceptible effect. A sketch is here given of

two young leaves which had naturally caught hold of two thin

branches. A forked twig placed so as to press lightly on the under

side of a young footstalk caused it, in 12 hrs., to bend greatly, and

ultimately to such an extent that the leaf passed to the opposite

side of the stem; the forked stick having been removed, the leaf

slowly recovered its former position.

The young leaves spontaneously and gradually change their position:

when first developed the petioles are upturned and parallel to the

stem; they then slowly bend downwards, remaining for a short time at

right angles to the stem, and then become so much arched downwards

that the blade of the leaf points to the ground with its tip curled

inwards, so that the whole petiole and leaf together form a hook.

They are thus enabled to catch hold of any twig with which they may

be brought into contact by the revolving movement of the internodes.

If this does not happen, they retain their hooked shape for a

considerable time, and then bending upwards reassume their original

upturned position, which is preserved ever afterwards. The petioles

which have clasped any object soon become much thickened and

strengthened, as may be seen in the drawing.

Clematis montana.--The long, thin petioles of the leaves, whilst

young, are sensitive, and when lightly rubbed bend to the rubbed

side, subsequently becoming straight. They are far more sensitive

than the petioles of C. glandulosa; for a loop of thread weighing a

quarter of a grain (16.2 mg.) caused them to bend; a loop weighing

only one-eighth of a grain (8.1 mg.) sometimes acted and sometimes

did not act. The sensitiveness extends from the blade of the leaf to

the stem. I may here state that I ascertained in all cases the

weights of the string and thread used by carefully weighing 50 inches

in a chemical balance, and then cutting off measured lengths. The

main petiole carries three leaflets; but their short, sub-petioles

are not sensitive. A young, inclined shoot (the plant being in the

greenhouse) made a large circle opposed to the course of the sun in 4

hrs. 20 m., but the next day, being very cold, the time was 5 hrs. 10

m. A stick placed near a revolving stem was soon struck by the

petioles which stand out at right angles, and the revolving movement

was thus arrested. The petioles then began, being excited by the

contact, to slowly wind round the stick. When the stick was thin, a

petiole sometimes wound twice round it. The opposite leaf was in no

way affected. The attitude assumed by the stem after the petiole had

clasped the stick, was that of a man standing by a column, who throws

his arm horizontally round it. With respect to the stem's power of

twining, some remarks will be made under C. calycina.

Clematis Sieboldi.--A shoot made three revolutions against the sun at

an average rate of 3 hrs. 11 m. The power of twining is like that of

the last species. Its leaves are nearly similar in structure and in

function, excepting that the sub-petioles of the lateral and terminal

leaflets are sensitive. A loop of thread, weighing one-eighth of a

grain, acted on the main petiole, but not until two or three days had

elapsed. The leaves have the remarkable habit of spontaneously

revolving, generally in vertical ellipses, in the same manner, but in

a less degree, as will be described under C. microphylla.

Clematis calycina.--The young shoots are thin and flexible: one

revolved, describing a broad oval, in 5 hrs. 30 m., and another in 6

hrs. 12 m. They followed the course of the sun; but the course, if

observed long enough, would probably be found to vary in this

species, as well as in all the others of the genus. It is a rather

better twiner than the two last species: the stem sometimes made two

spiral turns round a thin stick, if free from twigs; it then ran

straight up for a space, and reversing its course took one or two

turns in an opposite direction. This reversal of the spire occurred

in all the foregoing species. The leaves are so small compared with

those of most of the other species, that the petioles at first seem

ill-adapted for clasping. Nevertheless, the main service of the

revolving movement is to bring them into contact with surrounding

objects, which are slowly but securely seized. The young petioles,

which alone are sensitive, have their ends bowed a little downwards,

so as to be in a slight degree hooked; ultimately the whole leaf, if

it catches nothing, becomes level. I gently rubbed with a thin twig

the lower surfaces of two young petioles; and in 2 hrs. 30 m. they

were slightly curved downwards; in 5 hrs., after being rubbed, the

end of one was bent completely back, parallel to the basal portion;

in 4 hrs. subsequently it became nearly straight again. To show how

sensitive the young petioles are, I may mention that I just touched

the under sides of two with a little water-colour, which when dry

formed an excessively thin and minute crust; but this sufficed in 24

hrs. to cause both to bend downwards. Whilst the plant is young,

each leaf consists of three divided leaflets, which barely have

distinct petioles, and these are not sensitive; but when the plant is

well grown, the petioles of the two lateral and terminal leaflets are

of considerable length, and become sensitive so as to be capable of

clasping an object in any direction.

When a petiole has clasped a twig, it undergoes some remarkable

changes, which may be observed with the other species, but in a less

strongly marked manner, and will here be described once for all. The

clasped petiole in the course of two or three days swells greatly,

and ultimately becomes nearly twice as thick as the opposite one

which has clasped nothing. When thin transverse slices of the two

are placed under the microscope their difference is conspicuous: the

side of the petiole which has been in contact with the support, is

formed of a layer of colourless cells with their longer axes directed

from the centre, and these are very much larger than the

corresponding cells in the opposite or unchanged petiole; the central

cells, also, are in some degree enlarged, and the whole is much

indurated. The exterior surface generally becomes bright red. But a

far greater change takes place in the nature of the tissues than that

which is visible: the petiole of the unclasped leaf is flexible and

can be snapped easily, whereas the clasped one acquires an

extraordinary degree of toughness and rigidity, so that considerable

force is required to pull it into pieces. With this change, great

durability is probably acquired; at least this is the case with the

clasped petioles of Clematis vitalba. The meaning of these changes

is obvious, namely, that the petioles may firmly and durably support

the stem.

Clematis microphylla, var. leptophylla.--The long and thin internodes

of this Australian species revolve sometimes in one direction and

sometimes in an opposite one, describing long, narrow, irregular

ellipses or large circles. Four revolutions were completed within

five minutes of the same average rate of 1 hr. 51 m.; so that this

species moves more quickly than the others of the genus. The shoots,

when placed near a vertical stick, either twine round it, or clasp it

with the basal portions of their petioles. The leaves whilst young

are nearly of the same shape as those of C. viticella, and act in the

same manner like a hook, as will be described under that species.

But the leaflets are more divided, and each segment whilst young

terminates in a hardish point, which is much curved downwards and

inwards; so that the whole leaf readily catches hold of any

neighbouring object. The petioles of the young terminal leaflets are

acted on by loops of thread weighing 0.125th and even 0.0625th of a

grain. The basal portion of the main petiole is much less sensitive,

but will clasp a stick against which it presses.

The leaves, whilst young, are continually and spontaneously moving

slowly. A bell-glass was placed over a shoot secured to a stick, and

the movements of the leaves were traced on it during several days. A

very irregular line was generally formed; but one day, in the course

of eight hours and three quarters, the figure clearly represented

three and a half irregular ellipses, the most perfect one of which

was completed in 2 hrs. 35 m. The two opposite leaves moved

independently of each other. This movement of the leaves would aid

that of the internodes in bringing the petioles into contact with

surrounding objects. I discovered this movement too late to be

enabled to observe it in the other species; but from analogy I can

hardly doubt that the leaves of at least C. viticella, C. flammula,

and C. vitalba move spontaneously; and, judging from C Sieboldi, this

probably is the case with C. montana and C. calycina. I ascertained

that the simple leaves of C. glandulosa exhibited no spontaneous

revolving movement.

Clematis viticella, var. venosa.--In this and the two following

species the power of spirally twining is completely lost, and this

seems due to the lessened flexibility of the internodes and to the

interference caused by the large size of the leaves. But the

revolving movement, though restricted, is not lost. In our present

species a young internode, placed in front of a window, made three

narrow ellipses, transversely to the direction of the light, at an

average rate of 2 hrs. 40 m. When placed so that the movements were

to and from the light, the rate was greatly accelerated in one half

of the course, and retarded in the other, as with twining plants.

The ellipses were small; the longer diameter, described by the apex

of a shoot bearing a pair of not expanded leaves, was only 4.625

inches, and that by the apex of the penultimate internode only 1.125

inch. At the most favourable period of growth each leaf would hardly

be carried to and fro by the movement of the internodes more than two

or three inches, but, as above stated, it is probable that the leaves

themselves move spontaneously. The movement of the whole shoot by

the wind and by its rapid growth, would probably be almost equally

efficient as these spontaneous movements, in bringing the petioles

into contact with surrounding objects.

The leaves are of large size. Each bears three pairs of lateral

leaflets and a terminal one, all supported on rather long sub-

petioles. The main petiole bends a little angularly downwards at

each point where a pair of leaflets arises (see fig. 2), and the

petiole of the terminal leaflet is bent downwards at right angles;

hence the whole petiole, with its rectangularly bent extremity, acts

as a hook. This hook, the lateral petioles being directed a little

upwards; forms an excellent grappling apparatus, by which the leaves

readily become entangled with surrounding objects. If they catch

nothing, the whole petiole ultimately grows straight. The main

petiole, the sub-petioles, and the three branches into which each

basi-lateral sub-petiole is generally subdivided, are all sensitive.

The basal portion of the main petiole, between the stem and the first

pair of leaflets, is less sensitive than the remainder; it will,

however, clasp a stick with which it is left in contact. The

inferior surface of the rectangularly bent terminal portion (carrying

the terminal leaflet), which forms the inner side of the end of the

hook, is the most sensitive part; and this portion is manifestly best

adapted to catch a distant support. To show the difference in

sensibility, I gently placed loops of string of the same weight (in

one instance weighing only 0.82 of a grain or 53.14 mg.) on the

several lateral sub-petioles and on the terminal one; in a few hours

the latter was bent, but after 24 hrs. no effect was produced on the

other sub-petioles. Again, a terminal sub-petiole placed in contact

with a thin stick became sensibly curved in 45 m., and in 1 hr. 10m.

moved through ninety degrees; whilst a lateral sub-petiole did not

become sensibly curved until 3 hrs. 30 m. had elapsed. In all cases,

if the sticks are taken away, the petioles continue to move during

many hours afterwards; so they do after a slight rubbing; but they

become straight again, after about a day's interval, that is if the

flexure has not been very great or long continued.

The graduated difference in the extension of the sensitiveness in the

petioles of the above-described species deserves notice. In C.

montana it is confined to the main petiole, and has not spread to the

sub-petioles of the three leaflets; so it is with young plants of C.

calycina, but in older plants it spreads to the three sub-petioles.

In C. viticella the sensitiveness has spread to the petioles of the

seven leaflets, and to the subdivisions of the basi-lateral sub-

petioles. But in this latter species it has diminished in the basal

part of the main petiole, in which alone it resided in C. montana;

whilst it has increased in the abruptly bent terminal portion.

Clematis flammula.--The rather thick, straight, and stiff shoots,

whilst growing vigorously in the spring, make small oval revolutions,

following the sun in their course. Four were made at an average rate

of 3 hrs. 45 m. The longer axis of the oval, described by the

extreme tip, was directed at right angles to the line joining the

opposite leaves; its length was in one case only 1.375, and in

another case 1.75 inch; so that the young leaves were moved a very

short distance. The shoots of the same plant observed in midsummer,

when growing not so quickly, did not revolve at all. I cut down

another plant in the early summer, so that by August 1st it had

formed new and moderately vigorous shoots; these, when observed under

a bell-glass, were on some days quite stationary, and on other days

moved to and fro only about the eighth of an inch. Consequently the

revolving power is much enfeebled in this species, and under

unfavourable circumstances is completely lost. The shoot must depend

for coming into contact with surrounding objects on the probable,

though not ascertained spontaneous movement of the leaves, on rapid

growth, and on movement from the wind. Hence, perhaps, it is that

the petioles have acquired a high degree of sensitiveness as a

compensation for the little power of movement in the shoots.

The petioles are bowed downwards, and have the same general hook-like

form as in C. viticella. The medial petiole and the lateral sub-

petioles are sensitive, especially the much bent terminal portion.

As the sensitiveness is here greater than in any other species of the

genus observed by me, and is in itself remarkable, I will give fuller

details. The petioles, when so young that they have not separated

from one another, are not sensitive; when the lamina of a leaflet has

grown to a quarter of an inch in length (that is, about one-sixth of

its full size), the sensitiveness is highest; but at this period the

petioles are relatively much more fully developed than are the blades

of the leaves. Full-grown petioles are not in the least sensitive.

A thin stick placed so as to press lightly against a petiole, having

a leaflet a quarter of an inch in length, caused the petiole to bend

in 3 hrs. 15 m. In another case a petiole curled completely round a

stick in 12 hrs. These petioles were left curled for 24 hrs., and the

sticks were then removed; but they never straightened themselves. I

took a twig, thinner than the petiole itself, and with it lightly

rubbed several petioles four times up and down; these in 1 hr. 45 m.

became slightly curled; the curvature increased during some hours and

then began to decrease, but after 25 hrs. from the time of rubbing a

vestige of the curvature remained. Some other petioles similarly

rubbed twice, that is, once up and once down, became perceptibly

curved in about 2 hrs. 30 m., the terminal sub-petiole moving more

than the lateral sub-petioles; they all became straight again in

between 12 hrs. and 14 hrs. Lastly, a length of about one-eighth of

an inch of a sub-petiole, was lightly rubbed with the same twig only

once; it became slightly curved in 3 hrs., remaining so during 11

hrs., but by the next morning was quite straight.

The following observations are more precise. After trying heavier

pieces of string and thread, I placed a loop of fine string, weighing

1.04 gr. (67.4 mg.) on a terminal sub-petiole: in 6 hrs. 40 m. a

curvature could be seen; in 24 hrs. the petiole formed an open ring

round the string; in 48 hrs. the ring had almost closed on the

string, and in 72 hrs. seized it so firmly, that some force was

necessary for its withdrawal. A loop weighing 0.52 of a grain (33.7

mg.) caused in 14 hrs. a lateral sub-petiole just perceptibly to

curve, and in 24 hrs. it moved through ninety degrees. These

observations were made during the summer: the following were made in

the spring, when the petioles apparently are more sensitive:- A loop

of thread, weighing one-eighth of a grain (8.1 mg.), produced no

effect on the lateral sub-petioles, but placed on a terminal one,

caused it, after 24 hrs., to curve moderately; the curvature, though

the loop remained suspended, was after 48 hrs. diminished, but never

disappeared; showing that the petiole had become partially accustomed

to the insufficient stimulus. This experiment was twice repeated

with nearly the same result. Lastly, a loop of thread, weighing only

one-sixteenth of a grain (4.05 mg.) was twice gently placed by a

forceps on a terminal sub-petiole (the plant being, of course, in a

still and closed room), and this weight certainly caused a flexure,

which very slowly increased until the petiole moved through nearly

ninety degrees: beyond this it did not move; nor did the petiole,

the loop remaining suspended, ever become perfectly straight again.

When we consider, on the one hand, the thickness and stiffness of the

petioles, and, on the other hand, the thinness and softness of fine

cotton thread, and what an extremely small weight one-sixteenth of a

grain (4.05 mg.) is, these facts are remarkable. But I have reason

to believe that even a less weight excites curvature when pressing

over a broader surface than that acted on by a thread. Having

noticed that the end of a suspended string which accidentally touched

a petiole, caused it to bend, I took two pieces of thin twine, 10

inches in length (weighing 1.64 gr.), and, tying them to a stick, let

them hang as nearly perpendicularly downwards as their thinness and

flexuous form, after being stretched, would permit; I then quietly

placed their ends so as just to rest on two petioles, and these

certainly became curved in 36 hrs. One of the ends touched the angle

between a terminal and lateral sub-petiole, and it was in 48 hours

caught between them as by a forceps. In these cases the pressure,

though spread over a wider surface than that touched by the cotton

thread, must have been excessively slight.

Clematis vitalba.--The plants were in pots and not healthy, so that I

dare not trust my observations, which indicate much similarity in

habits with C. flammula. I mention this species only because I have

seen many proofs that the petioles in a state of nature are excited

to movement by very slight pressure. For instance, I have found them

embracing thin withered blades of grass, the soft young leaves of a

maple, and the flower-peduncles of the quaking-grass or Briza. The

latter are about as thick as the hair of a man's beard, but they were

completely surrounded and clasped. The petioles of a leaf, so young

that none of the leaflets were expanded, had partially seized a twig.

Those of almost all the old leaves, even when unattached to any

object, are much convoluted; but this is owing to their having come,

whilst young, into contact during several hours with some object

subsequently removed. With none of the above-described species,

cultivated in pots and carefully observed, was there any permanent

bending of the petioles without the stimulus of contact. In winter,

the blades of the leaves of C. vitalba drop off; but the petioles (as

was observed by Mohl) remain attached to the branches, sometimes

during two seasons; and, being convoluted, they curiously resemble

true tendrils, such as those possessed by the allied genus Naravelia.

The petioles which have clasped some object become much more stiff,

hard, and polished than those which have failed in this their proper

function.

TROPAEOLUM.--I observed T. tricolorum, T. azureum, T. pentaphyllum,

T. peregrinum, T. elegans, T. tuberosum, and a dwarf variety of, as I

believe, T. minus.

Tropaeolum tricolorum, var. grandiflorum.--The flexible shoots, which

first rise from the tubers, are as thin as fine twine. One such

shoot revolved in a course opposed to the sun, at an average rate,

judging from three revolutions, of 1 hr. 23 m.; but no doubt the

direction of the revolving movement is variable. When the plants

have grown tall and are branched, all the many lateral shoots

revolve. The stem, whilst young, twines regularly round a thin

vertical stick, and in one case I counted eight spiral turns in the

same direction; but when grown older, the stem often runs straight up

for a space, and, being arrested by the clasping petioles, makes one

or two spires in a reversed direction. Until the plant grows to a

height of two or three feet, requiring about a month from the time

when the first shoot appears above ground, no true leaves are

produced, but, in their place, filaments coloured like the stem. The

extremities of these filaments are pointed, a little flattened, and

furrowed on the upper surface. They never become developed into

leaves. As the plant grows in height new filaments are produced with

slightly enlarged tips; then others, bearing on each side of the

enlarged medial tip a rudimentary segment of a leaf; soon other

segments appear, and at last a perfect leaf is formed, with seven

deep segments. So that on the same plant we may see every step, from

tendril-like clasping filaments to perfect leaves with clasping

petioles. After the plant has grown to a considerable height, and is

secured to its support by the petioles of the true leaves, the

clasping filaments on the lower part of the stem wither and drop off;

so that they perform only a temporary service.

These filaments or rudimentary leaves, as well as the petioles of the

perfect leaves, whilst young, are highly sensitive on all sides to a

touch. The slightest rub caused them to curve towards the rubbed

side in about three minutes, and one bent itself into a ring in six

minutes; they subsequently became straight. When, however, they have

once completely clasped a stick, if this is removed, they do not

straighten themselves. The most remarkable fact, and one which I

have observed in no other species of the genus, is that the filaments

and the petioles of the young leaves, if they catch no object, after

standing for some days in their original position, spontaneously and

slowly oscillate a little from side to side, and then move towards

the stem and clasp it. They likewise often become, after a time, in

some degree spirally contracted. They therefore fully deserve to be

called tendrils, as they are used for climbing, are sensitive to a

touch, move spontaneously, and ultimately contract into a spire,

though an imperfect one. The present species would have been classed

amongst the tendril-bearers, had not these characters been confined

to early youth. During maturity it is a true leaf-climber.

Tropaeolum azureum.--An upper internode made four revolutions,

following the sun, at an average rate of 1 hr. 47 m. The stem twined

spirally round a support in the same irregular manner as that of the

last species. Rudimentary leaves or filaments do not exist. The

petioles of the young leaves are very sensitive: a single light rub

with a twig caused one to move perceptibly in 5 m., and another in 6

m. The former became bent at right angles in 15 min., and became

straight again in between 5 hrs. and 6 hrs. A loop of thread

weighing 0.125th of a grain caused another petiole to curve.

Tropaeolum pentaphyllum.--This species has not the power of spirally

twining, which seems due, not so much to a want of flexibility in the

stem, as to continual interference from the clasping petioles. An

upper internode made three revolutions, following the sun, at an

average rate of 1 hr. 46 m. The main purpose of the revolving

movement in all the species of Tropaeolum manifestly is to bring the

petioles into contact with some supporting object. The petiole of a

young leaf, after a slight rub, became curved in 6 m.; another, on a

cold day, in 20 m., and others in from 8 m. to 10 m. Their curvature

usually increased greatly in from 15 m. to 20 m., and they became

straight again in between 5 hrs. and 6 hrs., but on one occasion in 3

hrs. When a petiole has fairly clasped a stick, it is not able, on

the removal of the stick, to straighten itself. The free upper part

of one, the base of which had already clasped a stick, still retained

the power of movement. A loop of thread weighing 0.125th of a grain

caused a petiole to curve; but the stimulus was not sufficient, the

loop remaining suspended, to cause a permanent flexure. If a much

heavier loop be placed in the angle between the petiole and the stem,

it produces no effect; whereas we have seen with Clematis montana

that the angle between the stem and petiole is sensitive.

Tropaeolum peregrinum.--The first-formed internodes of a young plant

did not revolve, resembling in this respect those of a twining plant.

In an older plant the four upper internodes made three irregular

revolutions, in a course opposed to the sun, at an average rate of 1

hr. 48 min. It is remarkable that the average rate of revolution

(taken, however, but from few observations) is very nearly the same

in this and the two last species, namely, 1 hr. 47 m., 1 hr. 46 m.,

and 1 hr. 48 m. The present species cannot twine spirally, which

seems mainly due to the rigidity of the stem. In a very young plant,

which did not revolve, the petioles were not sensitive. In older

plants the petioles of quite young leaves, and of leaves as much as

an inch and a quarter in diameter, are sensitive. A moderate rub

caused one to curve in 10 m., and others in 20 m. They became

straight again in between 5 hrs. 45m. and 8 hrs. Petioles which have

naturally come into contact with a stick, sometimes take two turns

round it. After they have clasped a support, they become rigid and

hard. They are less sensitive to a weight than in the previous

species; for loops of string weighing 0.82 of a grain (53.14 mg.),

did not cause any curvature, but a loop of double this weight (1.64

gr.) acted.

Tropaeolum elegans.--I did not make many observations on this

species. The short and stiff internodes revolve irregularly,

describing small oval figures. One oval was completed in 3 hrs. A

young petiole, when rubbed, became slightly curved in 17 m.; and

afterwards much more so. It was nearly straight again in 8 hrs.

Tropaeolum tuberosum.--On a plant nine inches in height, the

internodes did not move at all; but on an older plant they moved

irregularly and made small imperfect ovals. These movements could be

detected only by being traced on a bell-glass placed over the plant.

Sometimes the shoots stood still for hours; during some days they

moved only in one direction in a crooked line; on other days they

made small irregular spires or circles, one being completed in about

4 hrs. The extreme points reached by the apex of the shoot were only

about one or one and a half inches asunder; yet this slight movement

brought the petioles into contact with some closely surrounding

twigs, which were then clasped. With the lessened power of

spontaneously revolving, compared with that of the previous species,

the sensitiveness of the petioles is also diminished. These, when

rubbed a few times, did not become curved until half an hour had

elapsed; the curvature increased during the next two hours, and then

very slowly decreased; so that they sometimes required 24 hrs. to

become straight again. Extremely young leaves have active petioles;

one with the lamina only 0.15 of an inch in diameter, that is, about

a twentieth of the full size, firmly clasped a thin twig. But leaves

grown to a quarter of their full size can likewise act.

Tropaeolum minus (?).--The internodes of a variety named "dwarf

crimson Nasturtium" did not revolve, but moved in a rather irregular

course during the day to the light, and from the light at night. The

petioles, when well rubbed, showed no power of curving; nor could I

see that they ever clasped any neighbouring object. We have seen in

this genus a gradation from species such as T. tricolorum, which have

extremely sensitive petioles, and internodes which rapidly revolve

and spirally twine up a support, to other species such as T. elegans

and T. tuberosum, the petioles of which are much less sensitive, and

the internodes of which have very feeble revolving powers and cannot

spirally twine round a support, to this last species, which has

entirely lost or never acquired these faculties. From the general

character of the genus, the loss of power seems the more probable

alternative.

In the present species, in T. elegans, and probably in others, the

flower-peduncle, as soon as the seed-capsule begins to swell,

spontaneously bends abruptly downwards and becomes somewhat

convoluted. If a stick stands in the way, it is to a certain extent

clasped; but, as far as I have been able to observe, this clasping

movement is independent of the stimulus from contact.

ANTIRRHINEAE.--In this tribe (Lindley) of the Scrophulariaceae, at

least four of the seven included genera have leaf-climbing species.

Maurandia Barclayana.--A thin, slightly bowed shoot made two

revolutions, following the sun, each in 3 hrs. 17 min.; on the

previous day this same shoot revolved in an opposite direction. The

shoots do not twine spirally, but climb excellently by the aid of

their young and sensitive petioles. These petioles, when lightly

rubbed, move after a considerable interval of time, and subsequently

become straight again. A loop of thread weighing 0.125th of a grain

caused them to bend.

Maurandia semperflorens.--This freely growing species climbs exactly

like the last, by the aid of its sensitive petioles. A young

internode made two circles, each in 1 hr. 46 mm.; so that it moved

almost twice as rapidly as the last species. The internodes are not

in the least sensitive to a touch or pressure. I mention this

because they are sensitive in a closely allied genus, namely,

Lophospermum. The present species is unique in one respect. Mohl

asserts (p. 45) that "the flower-peduncles, as well as the petioles,

wind like tendrils;" but he classes as tendrils such objects as the

spiral flower-stalks of the Vallisneria. This remark, and the fact

of the flower-peduncles being decidedly flexuous, led me carefully to

examine them. They never act as true tendrils; I repeatedly placed

thin sticks in contact with young and old peduncles, and I allowed

nine vigorous plants to grow through an entangled mass of branches;

but in no one instance did they bend round any object. It is indeed

in the highest degree improbable that this should occur, for they are

generally developed on branches which have already securely clasped a

support by the petioles of their leaves; and when borne on a free

depending branch, they are not produced by the terminal portion of

the internode which alone has the power of revolving; so that they

could be brought only by accident into contact with any neighbouring

object. Nevertheless (and this is the remarkable fact) the flower-

peduncles, whilst young, exhibit feeble revolving powers, and are

slightly sensitive to a touch. Having selected some stems which had

firmly clasped a stick by their petioles, and having placed a bell-

glass over them, I traced the movements of the young flower-

peduncles. The tracing generally formed a short and extremely

irregular line, with little loops in its course. A young peduncle

1.5 inch in length was carefully observed during a whole day, and it

made four and a half narrow, vertical, irregular, and short ellipses-

-each at an average rate of about 2 hrs. 25 m. An adjoining peduncle

described during the same time similar, though fewer, ellipses. As

the plant had occupied for some time exactly the same position, these

movements could not be attributed to any change in the action of the

light. Peduncles, old enough for the coloured petals to be just

visible, do not move. With respect to irritability, {21} I rubbed

two young peduncles (1.5 inch in length) a few times very lightly

with a thin twig; one was rubbed on the upper, and the other on the

lower side, and they became in between 4 hrs. and 5 hrs. distinctly

bowed towards these sides; in 24 hrs. subsequently, they straightened

themselves. Next day they were rubbed on the opposite sides, and

they became perceptibly curved towards these sides. Two other and

younger peduncles (three-fourths of an inch in length) were lightly

rubbed on their adjoining sides, and they became so much curved

towards one another, that the arcs of the bows stood at nearly right

angles to their previous direction; and this was the greatest

movement seen by me. Subsequently they straightened themselves.

Other peduncles, so young as to be only three-tenths of an inch in

length, became curved when rubbed. On the other hand, peduncles

above 1.5 inch in length required to be rubbed two or three times,

and then became only just perceptibly bowed. Loops of thread

suspended on the peduncles produced no effect; loops of string,

however, weighing 0.82 and 1.64 of a grain sometimes caused a slight

curvature; but they were never closely clasped, as were the far

lighter loops of thread by the petioles.

In the nine vigorous plants observed by me, it is certain that

neither the slight spontaneous movements nor the slight sensitiveness

of the flower-peduncles aided the plants in climbing. If any member

of the Scrophulariaceae had possessed tendrils produced by the

modification of flower-peduncles, I should have thought that this

species of Maurandia had perhaps retained a useless or rudimentary

vestige of a former habit; but this view cannot be maintained. We

may suspect that, owing to the principle of correlation, the power of

movement has been transferred to the flower-peduncles from the young

internodes, and sensitiveness from the young petioles. But to

whatever cause these capacities are due, the case is interesting;

for, by a little increase in power through natural selection, they

might easily have been rendered as useful to the plant in climbing,

as are the flower-peduncles (hereafter to be described) of Vitis or

Cardiospermum.

Rhodochiton volubile.--A long flexible shoot swept a large circle,

following the sun, in 5 hrs. 30 m.; and, as the day became warmer, a

second circle was completed in 4 hrs. 10 m. The shoots sometimes

make a whole or a half spire round a vertical stick, they then run

straight up for a space, and afterwards turn spirally in an opposite

direction. The petioles of very young leaves about one-tenth of

their full size, are highly sensitive, and bend towards the side

which is touched; but they do not move quickly. One was perceptibly

curved in 1 hr. 10 m., after being lightly rubbed, and became

considerably curved in 5 hrs. 40 m.; some others were scarcely curved

in 5 hrs. 30 m., but distinctly so in 6 hrs. 30 m. A curvature was

perceptible in one petiole in between 4 hrs. 30 m. and 5 hrs., after

the suspension of a little loop of string. A loop of fine cotton

thread, weighing one sixteenth of a grain (4.05 mg.), not only caused

a petiole slowly to bend, but was ultimately so firmly clasped that

it could be withdrawn only by some little force. The petioles, when

coming into contact with a stick, take either a complete or half a

turn round it, and ultimately increase much in thickness. They do

not possess the power of spontaneously revolving.

Lophospermum scandens, var. purpureum.--Some long, moderately thin

internodes made four revolutions at an average rate of 3 hrs. 15 m.

The course pursued was very irregular, namely, an extremely narrow

ellipse, a large circle, an irregular spire or a zigzag line, and

sometimes the apex stood still. The young petioles, when brought by

the revolving movement into contact with sticks, clasped them, and

soon increased considerably in thickness. But they are not quite so

sensitive to a weight as those of the Rhodochiton, for loops of

thread weighing one-eighth of a grain did not always cause them to

bend.

This plant presents a case not observed by me in any other leaf-

climber or twiner, {22} namely, that the young internodes of the stem

are sensitive to a touch. When a petiole of this species clasps a

stick, it draws the base of the internode against it; and then the

internode itself bends towards the stick, which is caught between the

stem and the petiole as by a pair of pincers. The internode

afterwards straightens itself, excepting the part in actual contact

with the stick. Young internodes alone are sensitive, and these are

sensitive on all sides along their whole length. I made fifteen

trials by twice or thrice lightly rubbing with a thin twig several

internodes; and in about 2 hrs., but in one case in 3 hrs., all were

bent: they became straight again in about 4 hrs. afterwards. An

internode, which was rubbed as often as six or seven times, became

just perceptibly curved in 1 hr. 15 m., and in 3 hrs. the curvature

increased much; it became straight again in the course of the

succeeding night. I rubbed some internodes one day on one side, and

the next day either on the opposite side or at right angles to the

first side; and the curvature was always towards the rubbed side.

According to Palm (p. 63), the petioles of Linaria cirrhosa and, to a

limited degree, those of L. elatine have the power of clasping a

support.

SOLANACEAE.--Solanum jasminoides.--Some of the species in this large

genus are twiners; but the present species is a true leaf-climber. A

long, nearly upright shoot made four revolutions, moving against the

sun, very regularly at an average rate of 3 hrs. 26 m. The shoots,

however, sometimes stood still. It is considered a greenhouse plant;

but when kept there, the petioles took several days to clasp a stick:

in the hothouse a stick was clasped in 7 hrs. In the greenhouse a

petiole was not affected by a loop of string, suspended during

several days and weighing 2.5 grains (163 mg.); but in the hothouse

one was made to curve by a loop weighing 1.64 gr. (106.27 mg.); and,

on the removal of the string, it became straight again. Another

petiole was not at all acted on by a loop weighing only 0.82 of a

grain (53.14 mg.) We have seen that the petioles of some other leaf-

climbing plants are affected by one-thirteenth of this latter weight.

In this species, and in no other leaf-climber seen by me, a full-

grown leaf is capable of clasping a stick; but in the greenhouse the

movement was so extraordinarily slow that the act required several

weeks; on each succeeding week it was clear that the petiole had

become more and more curved, until at last it firmly clasped the

stick.

The flexible petiole of a half or a quarter grown leaf which has

clasped an object for three or four days increases much in thickness,

and after several weeks becomes so wonderfully hard and rigid that it

can hardly be removed from its support. On comparing a thin

transverse slice of such a petiole with one from an older leaf

growing close beneath, which had not clasped anything, its diameter

was found to be fully doubled, and its structure greatly changed. In

two other petioles similarly compared, and here represented, the

increase in diameter was not quite so great. In the section of the

petiole in its ordinary state (A), we see a semilunar band of

cellular tissue (not well shown in the woodcut) differing slightly in

appearance from that outside it, and including three closely

approximate groups of dark vessels. Near the upper surface of the

petiole, beneath two exterior ridges, there are two other small

circular groups of vessels. In the section of the petiole (B) which

had clasped during several weeks a stick, the two exterior ridges

have become much less prominent, and the two groups of woody vessels

beneath them much increased in diameter. The semilunar band has been

converted into a complete ring of very hard, white, woody tissue,

with lines radiating from the centre. The three groups of vessels,

which, though near together, were before distinct, are now completely

blended. The upper part of this ring of woody vessels, formed by the

prolongation of the horns of the original semilunar band, is narrower

than the lower part, and slightly less compact. This petiole after

clasping the stick had actually become thicker than the stem from

which it arose; and this was chiefly due to the increased thickness

of the ring of wood. This ring presented, both in a transverse and

longitudinal section, a closely similar structure to that of the

stem. It is a singular morphological fact that the petiole should

thus acquire a structure almost identically the same with that of the

axis; and it is a still more singular physiological fact that so

great a change should have been induced by the mere act of clasping a

support. {23}

FUMARIACEAE.--Fumaria officinalis.--It could not have been

anticipated that so lowly a plant as this Fumaria should have been a

climber. It climbs by the aid of the main and lateral petioles of

its compound leaves; and even the much-flattened terminal portion of

the petiole can seize a support. I have seen a substance as soft as

a withered blade of grass caught. Petioles which have clasped any

object ultimately become rather thicker and more cylindrical. On

lightly rubbing several petioles with a twig, they became perceptibly

curved in 1 hr. 15 m., and subsequently straightened themselves. A

stick gently placed in the angle between two sub-petioles excited

them to move, and was almost clasped in 9 hrs. A loop of thread,

weighing one-eighth of a grain, caused, after 12 hrs. and before 20

hrs, had elapsed, a considerable curvature; but it was never fairly

clasped by the petiole. The young internodes are in continual

movement, which is considerable in extent, but very irregular; a

zigzag line, or a spire crossing itself; or a figure of 8 being

formed. The course during 12 hrs., when traced on a bell-glass,

apparently represented about four ellipses. The leaves themselves

likewise move spontaneously, the main petioles curving themselves in

accordance with the movements of the internodes; so that when the

latter moved to one side, the petioles moved to the same side, then,

becoming straight, reversed their curvature. The petioles, however,

do not move over a wide space, as could be seen when a shoot was

securely tied to a stick. The leaf in this case followed an

irregular course, like that made by the internodes.

Adlumia cirrhosa.--I raised some plants late in the summer; they

formed very fine leaves, but threw up no central stem. The first-

formed leaves were not sensitive; some of the later ones were so, but

only towards their extremities, which were thus enabled to clasp

sticks. This could be of no service to the plant, as these leaves

rose from the ground; but it showed what the future character of the

plant would have been, had it grown tall enough to climb. The tip of

one of these basal leaves, whilst young, described in 1 hr. 36 m. a

narrow ellipse, open at one end, and exactly three inches in length;

a second ellipse was broader, more irregular, and shorter, viz., only

2.5 inches in length, and was completed in 2 hrs. 2 m. From the

analogy of Fumaria and Corydalis, I have no doubt that the internodes

of Adlumia have the power of revolving.

Corydalis claviculata.--This plant is interesting from being in a

condition so exactly intermediate between a leaf-climber and a

tendril-bearer, that it might have been described under either head;

but, for reasons hereafter assigned, it has been classed amongst

tendril-bearers.

Besides the plants already described, Bignonia unguis and its close

allies, though aided by tendrils, have clasping petioles. According

to Mohl (p. 40), Cocculus Japonicus (one of the Menispermaceae) and a

fern, the Ophioglossum Japonicum (p. 39), climb by their leaf-stalks.

We now come to a small section of plants which climb by means of the

produced midribs or tips of their leaves.

LILIACEAE.--Gloriosa Plantii.--The stem of a half-grown plant

continually moved, generally describing an irregular spire, but

sometimes oval figures with the longer axes directed in different

lines. It either followed the sun, or moved in an opposite course,

and sometimes stood still before reversing its direction. One oval

was completed in 3 hrs. 40 m.; of two horseshoe-shaped figures, one

was completed in 4 hrs. 35 m. and the other in 3 hrs. The shoots, in

their movements, reached points between four and five inches asunder.

The young leaves, when first developed, stand up nearly vertically;

but by the growth of the axis, and by the spontaneous bending down of

the terminal half of the leaf, they soon become much inclined, and

ultimately horizontal. The end of the leaf forms a narrow, ribbon-

like, thickened projection, which at first is nearly straight, but by

the time the leaf gets into an inclined position, the end bends

downwards into a well-formed hook. This hook is now strong and rigid

enough to catch any object, and, when caught, to anchor the plant and

stop the revolving movement. Its inner surface is sensitive, but not

in nearly so high a degree as that of the many before-described

petioles; for a loop of string, weighing 1.64 grain, produced no

effect. When the hook has caught a thin twig or even a rigid fibre,

the point may be perceived in from 1 hr. to 3 hrs. to have curled a

little inwards; and, under favourable circumstances, it curls round

and permanently seizes an object in from 8 hrs. to 10 hrs. The hook

when first formed, before the leaf has bent downwards, is but little

sensitive. If it catches hold of nothing, it remains open and

sensitive for a long time; ultimately the extremity spontaneously and

slowly curls inwards, and makes a button-like, flat, spiral coil at

the end of the leaf. One leaf was watched, and the hook remained

open for thirty-three days; but during the last week the tip had

curled so much inwards that only a very thin twig could have been

inserted within it. As soon as the tip has curled so much inwards

that the hook is converted into a ring, its sensibility is lost; but

as long as it remains open some sensibility is retained.

Whilst the plant was only about six inches in height, the leaves,

four or five in number, were broader than those subsequently

produced; their soft and but little-attenuated tips were not

sensitive, and did not form hooks; nor did the stem then revolve. At

this early period of growth, the plant can support itself; its

climbing powers are not required, and consequently are not developed.

So again, the leaves on the summit of a full-grown flowering plant,

which would not require to climb any higher, were not sensitive and

could not clasp a stick. We thus see how perfect is the economy of

nature.

COMMELYNACEAE.--Flagellaria Indica.--From dried specimens it is

manifest that this plant climbs exactly like the Gloriosa. A young

plant 12 inches in height, and bearing fifteen leaves, had not a

single leaf as yet produced into a hook or tendril-like filament; nor

did the stem revolve. Hence this plant acquires its climbing powers

later in life than does the Gloriosa lily. According to Mohl (p.

41), Uvularia (Melanthaceae) also climbs like Gloriosa.

These three last-named genera are Monocotyledons; but there is one

Dicotyledon, namely Nepenthes, which is ranked by Mohl (p. 41)

amongst tendril-bearers; and I hear from Dr. Hooker that most of the

species climb well at Kew. This is effected by the stalk or midrib

between the leaf and the pitcher coiling round any support. The

twisted part becomes thicker; but I observed in Mr. Veitch's hothouse

that the stalk often takes a turn when not in contact with any

object, and that this twisted part is likewise thickened. Two

vigorous young plants of N. laevis and N. distillatoria, in my

hothouse, whilst less than a foot in height, showed no sensitiveness

in their leaves, and had no power of climbing. But when N. laevis

had grown to a height of 16 inches, there were signs of these powers.

The young leaves when first formed stand upright, but soon become

inclined; at this period they terminate in a stalk or filament, with

the pitcher at the extremity hardly at all developed. The leaves now

exhibited slight spontaneous movements; and when the terminal

filaments came into contact with a stick, they slowly bent round and

firmly seized it. But owing to the subsequent growth of the leaf,

this filament became after a time quite slack, though still remaining

firmly coiled round the stick. Hence it would appear that the chief

use of the coiling, at least whilst the plant is young, is to support

the pitcher with its load of secreted fluid.

Summary on Leaf-climbers.--Plants belonging to eight families are

known to have clasping petioles, and plants belonging to four

families climb by the tips of their leaves. In all the species

observed by me, with one exception, the young internodes revolve more

or less regularly, in some cases as regularly as those of a twining

plant. They revolve at various rates, in most cases rather rapidly.

Some few can ascend by spirally twining round a support. Differently

from most twiners, there is a strong tendency in the same shoot to

revolve first in one and then in an opposite direction. The object

gained by the revolving movement is to bring the petioles or the tips

of the leaves into contact with surrounding objects; and without this

aid the plant would be much less successful in climbing. With rare

exceptions, the petioles are sensitive only whilst young. They are

sensitive on all sides, but in different degrees in different plants;

and in some species of Clematis the several parts of the same petiole

differ much in sensitiveness. The hooked tips of the leaves of the

Gloriosa are sensitive only on their inner or inferior surfaces. The

petioles are sensitive to a touch and to excessively slight continued

pressure, even from a loop of soft thread weighing only the one-

sixteenth of a grain (4.05 mg.); and there is reason to believe that

the rather thick and stiff petioles of Clematis flammula are

sensitive to even much less weight if spread over a wide surface.

The petioles always bend towards the side which is pressed or

touched, at different rates in different species, sometimes within a

few minutes, but generally after a much longer period. After

temporary contact with any object, the petiole continues to bend for

a considerable time; afterwards it slowly becomes straight again, and

can then re-act. A petiole excited by an extremely slight weight

sometimes bends a little, and then becomes accustomed to the

stimulus, and either bends no more or becomes straight again, the

weight still remaining suspended. Petioles which have clasped an

object for some little time cannot recover their original position.

After remaining clasped for two or three days, they generally

increase much in thickness either throughout their whole diameter or

on one side alone; they subsequently become stronger and more woody,

sometimes to a wonderful degree; and in some cases they acquire an

internal structure like that of the stem or axis.

The young internodes of the Lophospermum as well as the petioles are

sensitive to a touch, and by their combined movement seize an object.

The flower-peduncles of the Maurandia semperflorens revolve

spontaneously and are sensitive to a touch, yet are not used for

climbing. The leaves of at least two, and probably of most, of the

species of Clematis, of Fumaria and Adlumia, spontaneously curve from

side to side, like the internodes, and are thus better adapted to

seize distant objects. The petioles of the perfect leaves of

Tropaeolum tricolorum, as well as the tendril-like filaments of the

plants whilst young, ultimately move towards the stem or the

supporting stick, which they then clasp. These petioles and

filaments also show some tendency to contract spirally. The tips of

the uncaught leaves of the Gloriosa, as they grow old, contract into

a flat spire or helix. These several facts are interesting in

relation to true tendrils.

With leaf climbers, as with twining plants, the first internodes

which rise from the ground do not, at least in the cases observed by

me, spontaneously revolve; nor are the petioles or tips of the first-

formed leaves sensitive. In certain species of Clematis, the large

size of the leaves, together with their habit of revolving, and the

extreme sensitiveness of their petioles, appear to render the

revolving movement of the internodes superfluous; and this latter

power has consequently become much enfeebled. In certain species of

Tropaeolum, both the spontaneous movements of the internodes and the

sensitiveness of the petioles have become much enfeebled, and in one

species have been completely lost.

CHAPTER III.--TENDRIL-BEARERS.

Nature of tendrils--BIGNONIACEAE, various species of, and their

different modes of climbing--Tendrils which avoid the light and creep

into crevices--Development of adhesive discs--Excellent adaptations

for seizing different kinds of supports.--POLEMONIACEAE--Cobaea

scandens much branched and hooked tendrils, their manner of action--

LEGUMINOSAE--COMPOSITAE--SMILACEAE--Smilax aspera, its inefficient

tendrils--FUMARIACEAE--Corydalis claviculata, its state intermediate

between that of a leaf-climber and a tendril-bearer.

By tendrils I mean filamentary organs, sensitive to contact and used

exclusively for climbing. By this definition, spines, hooks and

rootlets, all of which are used for climbing, are excluded. True

tendrils are formed by the modification of leaves with their

petioles, of flower-peduncles, branches, {24} and perhaps stipules.

Mohl, who includes under the name of tendrils various organs having a

similar external appearance, classes them according to their

homological nature, as being modified leaves, flower-peduncles, &c.

This would be an excellent scheme; but I observe that botanists are

by no means unanimous on the homological nature of certain tendrils.

Consequently I will describe tendril-bearing plants by natural

families, following Lindley's classification; and this will in most

cases keep those of the same nature together. The species to be

described belong to ten families, and will be given in the following

order: --Bignoniaceae, Polemoniaceae, Leguminosae, Compositae,

Smilaceae, Fumariaceae, Cucurbitaceae, Vitaceae, Sapindaceae,

Passifloraceae. {25}

BIGNONIACEAE.--This family contains many tendril-bearers, some

twiners, and some root-climbers. The tendrils always consist of

modified leaves. Nine species of Bignonia, selected by hazard, are

here described, in order to show what diversity of structure and

action there may be within the same genus, and to show what

remarkable powers some tendrils possess. The species, taken

together, afford connecting links between twiners, leaf-climbers,

tendril-bearers, and root-climbers.

Bignonia (an unnamed species from Kew, closely allied to B. unguis,

but with smaller and rather broader leaves).--A young shoot from a

cut-down plant made three revolutions against the sun, at an average

rate of 2 hrs. 6m. The stem is thin and flexible; it twined round a

slender vertical stick, ascending from left to right, as perfectly

and as regularly as any true twining-plant. When thus ascending, it

makes no use of its tendrils or petioles; but when it twined round a

rather thick stick, and its petioles were brought into contact with

it, these curved round the stick, showing that they have some degree

of irritability. The petioles also exhibit a slight degree of

spontaneous movement; for in one case they certainly described

minute, irregular, vertical ellipses. The tendrils apparently curve

themselves spontaneously to the same side with the petioles; but from

various causes, it was difficult to observe the movement of either

the tendrils or petioles, in this and the two following species. The

tendrils are so closely similar in all respects to those of B.

unguis, that one description will suffice.

Bignonia unguis.--The young shoots revolve, but less regularly and

less quickly than those of the last species. The stem twines

imperfectly round a vertical stick, sometimes reversing its

direction, in the same manner as described in so many leaf-climbers;

and this plant though possessing tendrils, climbs to a certain extent

like a leaf-climber. Each leaf consists of a petiole bearing a pair

of leaflets, and terminates in a tendril, which is formed by the

modification of three leaflets, and closely resembles that above

figured (fig. 5). But it is a little larger, and in a young plant

was about half an inch in length. It is curiously like the leg and

foot of a small bird, with the hind toe cut off. The straight leg or

tarsus is longer than the three toes, which are of equal length, and

diverging, lie in the same plane. The toes terminate in sharp, hard

claws, much curved downwards, like those on a bird's foot. The

petiole of the leaf is sensitive to contact; even a small loop of

thread suspended for two days caused it to bend upwards; but the sub-

petioles of the two lateral leaflets are not sensitive. The whole

tendril, namely, the tarsus and the three toes, are likewise

sensitive to contact, especially on their under surfaces. When a

shoot grows in the midst of thin branches, the tendrils are soon

brought by the revolving movement of the internodes into contact with

them; and then one toe of the tendril or more, commonly all three,

bend, and after several hours seize fast hold of the twigs, like a

bird when perched. If the tarsus of the tendril comes into contact

with a twig, it goes on slowly bending, until the whole foot is

carried quite round, and the toes pass on each side of the tarsus and

seize it. In like manner, if the petiole comes into contact with a

twig, it bends round, carrying the tendril, which then seizes its own

petiole or that of the opposite leaf. The petioles move

spontaneously, and thus, when a shoot attempts to twine round an

upright stick, those on both sides after a time come into contact

with it, and are excited to bend. Ultimately the two petioles clasp

the stick in opposite directions, and the foot-like tendrils, seizing

on each other or on their own petioles, fasten the stem to the

support with surprising security. The tendrils are thus brought into

action, if the stem twines round a thin vertical stick; and in this

respect the present species differs from the last. Both species use

their tendrils in the same manner when passing through a thicket.

This plant is one of the most efficient climbers which I have

observed; and it probably could ascend a polished stem incessantly

tossed by heavy storms. To show how important vigorous health is for

the action of all the parts, I may mention that when I first examined

a plant which was growing moderately well, though not vigorously, I

concluded that the tendrils acted only like the hooks on a bramble,

and that it was the most feeble and inefficient of all climbers!

Bignonia Tweedyana.--This species is closely allied to the last, and

behaves in the same manner; but perhaps twines rather better round a

vertical stick. On the same plant, one branch twined in one

direction and another in an opposite direction. The internodes in

one case made two circles, each in 2 hrs. 33 m. I was enabled to

observe the spontaneous movements of the petioles better in this than

in the two preceding species: one petiole described three small

vertical ellipses in the course of 11 hrs., whilst another moved in

an irregular spire. Some little time after a stem has twined round

an upright stick, and is securely fastened to it by the clasping

petioles and tendrils, it emits aerial roots from the bases of its

leaves; and these roots curve partly round and adhere to the stick.

This species of Bignonia, therefore, combines four different methods

of climbing generally characteristic of distinct plants, namely,

twining, leaf-climbing, tendril-climbing, and root-climbing.

In the three foregoing species, when the foot-like tendril has caught

an object, it continues to grow and thicken, and ultimately becomes

wonderfully strong, in the same manner as the petioles of leaf-

climbers. If the tendril catches nothing, it first slowly bends

downwards, and then its power of clasping is lost. Very soon

afterwards it disarticulates itself from the petiole, and drops off

like a leaf in autumn. I have seen this process of disarticulation

in no other tendrils, for these, when they fail to catch an object,

merely wither away.

Bignonia venusta.--The tendrils differ considerably from those of the

previous species. The lower part, or tarsus, is four times as long

as the three toes; these are of equal length and diverge equally, but

do not lie in the same plane; their tips are bluntly hooked, and the

whole tendril makes an excellent grapnel. The tarsus is sensitive on

all sides; but the three toes are sensitive only on their outer

surfaces. The sensitiveness is not much developed; for a slight

rubbing with a twig did not cause the tarsus or the toes to become

curved until an hour had elapsed, and then only in a slight degree.

Subsequently they straightened themselves. Both the tarsus and toes

can seize well hold of sticks. If the stem is secured, the tendrils

are seen spontaneously to sweep large ellipses; the two opposite

tendrils moving independently of one another. I have no doubt, from

the analogy of the two following allied species, that the petioles

also move spontaneously; but they are not irritable like those of B.

unguis and B. Tweedyana. The young internodes sweep large circles,

one being completed in 2 hrs. 15 m., and a second in 2 hrs. 55 m. By

these combined movements of the internodes, petioles, and grapnel-

like tendrils, the latter are soon brought into contact with

surrounding objects. When a shoot stands near an upright stick, it

twines regularly and spirally round it. As it ascends, it seizes the

stick with one of its tendrils, and, if the stick be thin, the right-

and left-hand tendrils are alternately used. This alternation

follows from the stem necessarily taking one twist round its own axis

for each completed circle.

The tendrils contract spirally a short time after catching any

object; those which catch nothing merely bend slowly downwards. But

the whole subject of the spiral contraction of tendrils will be

discussed after all the tendril-bearing species have been described.

Bignonia littoralis.--The young internodes revolve in large ellipses.

An internode bearing immature tendrils made two revolutions, each in

3 hrs. 50 m.; but when grown older with the tendrils mature, it made

two ellipses, each at the rate of 2 hrs. 44 m. This species, unlike

the preceding, is incapable of twining round a stick: this does not

appear to be due to any want of flexibility in the internodes or to

the action of the tendrils, and certainly not to any want of the

revolving power; nor can I account for the fact. Nevertheless the

plant readily ascends a thin upright stick by seizing a point above

with its two opposite tendrils, which then contract spirally. If the

tendrils seize nothing, they do not become spiral.

The species last described, ascended a vertical stick by twining

spirally and by seizing it alternately with its opposite tendrils,

like a sailor pulling himself up a rope, hand over hand; the present

species pulls itself up, like a sailor seizing with both hands

together a rope above his head.

The tendrils are similar in structure to those of the last species.

They continue growing for some time, even after they have clasped an

object. When fully grown, though borne by a young plant, they are 9

inches in length. The three divergent toes are shorter relatively to

the tarsus than in the former species; they are blunt at their tips

and but slightly hooked; they are not quite equal in length, the

middle one being rather longer than the others. Their outer surfaces

are highly sensitive; for when lightly rubbed with a twig, they

became perceptibly curved in 4 m. and greatly curved in 7 m. In 7

hrs. they became straight again and were ready to re-act. The

tarsus, for the space of one inch close to the toes, is sensitive,

but in a rather less degree than the toes; for the latter after a

slight rubbing, became curved in about half the time. Even the

middle part of the tarsus is sensitive to prolonged contact, as soon

as the tendril has arrived at maturity. After it has grown old, the

sensitiveness is confined to the toes, and these are only able to

curl very slowly round a stick. A tendril is perfectly ready to act,

as soon as the three toes have diverged, and at this period their

outer surfaces first become irritable. The irritability spreads but

little from one part when excited to another: thus, when a stick was

caught by the part immediately beneath the three toes, these seldom

clasped it, but remained sticking straight out.

The tendrils revolve spontaneously. The movement begins before the

tendril is converted into a three-pronged grapnel by the divergence

of the toes, and before any part has become sensitive; so that the

revolving movement is useless at this early period. The movement is,

also, now slow, two ellipses being completed conjointly in 24 hrs. 18

m. A mature tendril made an ellipse in 6 hrs.; so that it moved much

more slowly than the internodes. The ellipses which were swept, both

in a vertical and horizontal plane, were of large size. The petioles

are not in the least sensitive, but revolve like the tendrils. We

thus see that the young internodes, the petioles, and the tendrils

all continue revolving together, but at different rates. The

movements of the tendrils which rise opposite one another are quite

independent. Hence, when the whole shoot is allowed freely to

revolve, nothing can be more intricate than the course followed by

the extremity of each tendril. A wide space is thus irregularly

searched for some object to be grasped.

One other curious point remains to be mentioned. In the course of a

few days after the toes have closely clasped a stick, their blunt

extremities become developed, though not invariably, into irregular

disc-like balls which have the power of adhering firmly to the wood.

As similar cellular outgrowths will be fully described under B.

capreolata, I will here say nothing more about them.

Bignonia aequinoctialis, var. Chamberlaynii.--The internodes, the

elongated non-sensitive petioles, and the tendrils all revolve. The

stem does not twine, but ascends a vertical stick in the same manner

as the last species. The tendrils also resemble those of the last

species, but are shorter; the three toes are more unequal in length,

the two outer ones being about one-third shorter and rather thinner

than the middle toe; but they vary in this respect. They terminate

in small hard points; and what is important, cellular adhesive discs

are not developed. The reduced size of two of the toes as well as

their lessened sensitiveness, seem to indicate a tendency to

abortion; and on one of my plants the first-formed tendrils were

sometimes simple, that is, were not divided into three toes. We are

thus naturally led to the three following species with undivided

tendrils

Bignonia speciosa.--The young shoots revolve irregularly, making

narrow ellipses, spires or circles, at rates varying from 3 hrs. 30

m. to 4 hrs. 40 m.; but they show no tendency to twine. Whilst the

plant is young and does not require a support, tendrils are not

developed. Those borne by a moderately young plant were five inches

in length. They revolve spontaneously, as do the short and non-

sensitive petioles. When rubbed, they slowly bend to the rubbed side

and subsequently straighten themselves; but they are not highly

sensitive. There is something strange in their behaviour: I

repeatedly placed close to them, thick and thin, rough and smooth

sticks and posts, as well as string suspended vertically, but none of

these objects were well seized. After clasping an upright stick,

they repeatedly loosed it again, and often would not seize it at all,

or their extremities did not coil closely round. I have observed

hundreds of tendrils belonging to various Cucurbitaceous,

Passifloraceous, and Leguminous plants, and never saw one behave in

this manner. When, however, my plant had grown to a height of eight

or nine feet, the tendrils acted much better. They now seized a

thin, upright stick horizontally, that is, at a point on their own

level, and not some way up the stick as in the case of all the

previous species. Nevertheless, the non-twining stem was enabled by

this means to ascend the stick.

The extremity of the tendril is almost straight and sharp. The whole

terminal portion exhibits a singular habit, which in an animal would

be called an instinct; for it continually searches for any little

crevice or hole into which to insert itself. I had two young plants;

and, after having observed this habit, I placed near them posts,

which had been bored by beetles, or had become fissured by drying.

The tendrils, by their own movement and by that of the internodes,

slowly travelled over the surface of the wood, and when the apex came

to a hole or fissure it inserted itself; in order to effect this the

extremity for a length of half or quarter of an inch, would often

bend itself at right angles to the basal part. I have watched this

process between twenty and thirty times. The same tendril would

frequently withdraw from one hole and insert its point into a second

hole. I have also seen a tendril keep its point, in one case for 20

hrs. and in another for 36 hrs., in a minute hole, and then withdraw

it. Whilst the point is thus temporarily inserted, the opposite

tendril goes on revolving.

The whole length of a tendril often fits itself closely to any

surface of wood with which it has come into contact; and I have

observed one bent at right angles, from having entered a wide and

deep fissure, with its apex abruptly re-bent and inserted into a

minute lateral hole. After a tendril has clasped a stick, it

contracts spirally; if it remains unattached it hangs straight

downwards. If it has merely adapted itself to the inequalities of a

thick post, though it has clasped nothing, or if it has inserted its

apex into some little fissure, this stimulus suffices to induce

spiral contraction; but the contraction always draws the tendril away

from the post. So that in every case these movements, which seem so

nicely adapted for some purpose, were useless. On one occasion,

however, the tip became permanently jammed into a narrow fissure. I

fully expected, from the analogy of B. capreolata and B. littoralis,

that the tips would have been developed into adhesive discs; but I

could never detect even a trace of this process. There is therefore

at present something unintelligible about the habits of this plant.

Bignonia picta.--This species closely resembles the last in the

structure and movements of its tendrils. I also casually examined a

fine growing plant of the allied B. Lindleyi, and this apparently

behaved in all respects in the same manner.

Bignonia capreolata.--We now come to a species having tendrils of a

different type; but first for the internodes. A young shoot made

three large revolutions, following the sun, at an average rate of 2

hrs. 23 m. The stem is thin and flexible, and I have seen one make

four regular spiral turns round a thin upright stick, ascending of

course from right to left, and therefore in a reversed direction

compared with the before described species. Afterwards, from the

interference of the tendrils, it ascended either straight up the

stick or in an irregular spire. The tendrils are in some respects

highly remarkable. In a young plant they were about 2.5 inches in

length and much branched, the five chief branches apparently

representing two pairs of leaflets and a terminal one. Each branch

is, however, bifid or more commonly trifid towards the extremity,

with the points blunt yet distinctly hooked. A tendril bends to any

side which is lightly rubbed, and subsequently becomes straight

again; but a loop of thread weighing 0.25th of a grain produced no

effect. On two occasions the terminal branches became slightly

curved in 10 m. after they had touched a stick; and in 30 m. the tips

were curled quite round it. The basal part is less sensitive. The

tendrils revolved in an apparently capricious manner, sometimes very

slightly or not at all; at other times they described large regular

ellipses. I could detect no spontaneous movement in the petioles of

the leaves.

Whilst the tendrils are revolving more or less regularly, another

remarkable movement takes place, namely, a slow inclination from the

light towards the darkest side of the house. I repeatedly changed

the position of my plants, and some little time after the revolving

movement had ceased, the successively formed tendrils always ended by

pointing to the darkest side. When I placed a thick post near a

tendril, between it and the light, the tendril pointed in that

direction. In two instances a pair of leaves stood so that one of

the two tendrils was directed towards the light and the other to the

darkest side of the house; the latter did not move, but the opposite

one bent itself first upwards and then right over its fellow, so that

the two became parallel, one above the other, both pointing to the

dark: I then turned the plant half round; and the tendril which had

turned over recovered its original position, and the opposite one

which had not before moved, now turned over to the dark side.

Lastly, on another plant, three pairs of tendrils were produced at

the same time by three shoots, and all happened to be differently

directed: I placed the pot in a box open only on one side, and

obliquely facing the light; in two days all six tendrils pointed with

unerring truth to the darkest corner of the box, though to do this

each had to bend in a different manner. Six wind-vanes could not

have more truly shown the direction of the wind, than did these

branched tendrils the course of the stream of light which entered the

box. I left these tendrils undisturbed for above 24 hrs., and then

turned the pot half round; but they had now lost their power of

movement, and could not any longer avoid the light.

When a tendril has not succeeded in clasping a support, either

through its own revolving movement or that of the shoot, or by

turning towards any object which intercepts the light, it bends

vertically downwards and then towards its own stem, which it seizes

together with the supporting stick, if there be one. A little aid is

thus given in keeping the stem secure. If the tendril seizes

nothing, it does not contract spirally, but soon withers away and

drops off. If it seizes an object, all the branches contract

spirally.

I have stated that after a tendril has come into contact with a

stick, it bends round it in about half an hour; but I repeatedly

observed, as in the case of B. speciosa and its allies, that it often

again loosed the stick; sometimes seizing and loosing the same stick

three or four times. Knowing that the tendrils avoided the light, I

gave them a glass tube blackened within, and a well-blackened zinc

plate: the branches curled round the tube and abruptly bent

themselves round the edges of the zinc plate; but they soon recoiled

from these objects with what I can only call disgust, and

straightened themselves. I then placed a post with extremely rugged

bark close to a pair of tendrils; twice they touched it for an hour

or two, and twice they withdrew; at last one of the hooked

extremities curled round and firmly seized an excessively minute

projecting point of bark, and then the other branches spread

themselves out, following with accuracy every inequality of the

surface. I afterwards placed near the plant a post without bark but

much fissured, and the points of the tendrils crawled into all the

crevices in a beautiful manner. To my surprise, I observed that the

tips of the immature tendrils, with the branches not yet fully

separated, likewise crawled just like roots into the minutest

crevices. In two or three days after the tips had thus crawled into

the crevices, or after their hooked ends had seized minute points,

the final process, now to be described, commenced.

This process I discovered by having accidentally left a piece of wool

near a tendril; and this led me to bind a quantity of flax, moss, and

wool loosely round sticks, and to place them near tendrils. The wool

must not be dyed, for these tendrils are excessively sensitive to

some poisons. The hooked points soon caught hold of the fibres, even

loosely floating fibres, and now there was no recoiling; on the

contrary, the excitement caused the hooks to penetrate the fibrous

mass and to curl inwards, so that each hook caught firmly one or two

fibres, or a small bundle of them. The tips and the inner surfaces

of the hooks now began to swell, and in two or three days were

visibly enlarged. After a few more days the hooks were converted

into whitish, irregular balls, rather above the 0.05th of an inch

(1.27 mm.) in diameter, formed of coarse cellular tissue, which

sometimes wholly enveloped and concealed the hooks themselves. The

surfaces of these balls secrete some viscid resinous matter, to which

the fibres of the flax, &c., adhere. When a fibre has become

fastened to the surface, the cellular tissue does not grow directly

beneath it, but continues to grow closely on each side; so that when

several adjoining fibres, though excessively thin, were caught, so

many crests of cellular matter, each not as thick as a human hair,

grew up between them, and these, arching over on both sides, adhered

firmly together. As the whole surface of the ball continues to grow,

fresh fibres adhere and are afterwards enveloped; so that I have seen

a little ball with between fifty and sixty fibres of flax crossing it

at various angles and all embedded more or less deeply. Every

gradation in the process could be followed--some fibres merely

sticking to the surface, others lying in more or less deep furrows,

or deeply embedded, or passing through the very centre of the

cellular ball. The embedded fibres are so closely clasped that they

cannot be withdrawn. The outgrowing tissue has so strong a tendency

to unite, that two balls produced by distinct tendrils sometimes

unite and grow into a single one.

On one occasion, when a tendril had curled round a stick, half an

inch in diameter, an adhesive disc was formed; but this does not

generally occur in the case of smooth sticks or posts. If, however,

the tip catches a minute projecting point, the other branches form

discs, especially if they find crevices to crawl into. The tendrils

failed to attach themselves to a brick wall.

I infer from the adherence of the fibres to the discs or balls, that

these secrete some resinous adhesive matter; and more especially from

such fibres becoming loose if immersed in sulphuric ether. This

fluid likewise removes small, brown, glistening points which can

generally be seen on the surfaces of the older discs. If the hooked

extremities of the tendrils do not touch anything, discs, as far as I

have seen, are never formed; {26} but temporary contact during a

moderate time suffices to cause their development. I have seen eight

discs formed on the same tendril. After their development the

tendrils contract spirally, and become woody and very strong. A

tendril in this state supported nearly seven ounces, and would

apparently have supported a considerably greater weight, had not the

fibres of flax to which the discs were attached yielded.

From the facts now given, we may infer that though the tendrils of

this Bignonia can occasionally adhere to smooth cylindrical sticks

and often to rugged bark, yet that they are specially adapted to

climb trees clothed with lichens, mosses, or other such productions;

and I hear from Professor Asa Gray that the Polypodium incanum

abounds on the forest-trees in the districts of North America where

this species of Bignonia grows. Finally, I may remark how singular a

fact it is that a leaf should be metamorphosed into a branched organ

which turns from the light, and which can by its extremities either

crawl like roots into crevices, or seize hold of minute projecting

points, these extremities afterwards forming cellular outgrowths

which secrete an adhesive cement, and then envelop by their continued

growth the finest fibres.

Eccremocarpus scaber (Bignoniaceae).--Plants, though growing pretty

well in my green-house, showed no spontaneous movements in their

shoots or tendrils; but when removed to the hot-house, the young

internodes revolved at rates varying from 3 hrs. 15 m. to 1 hr. 13 m.

One large circle was swept at this latter unusually quick rate; but

generally the circles or ellipses were small, and sometimes the

course pursued was quite irregular. An internode, after making

several revolutions, sometimes stood still for 12 hrs. or 18 hrs.,

and then recommenced revolving. Such strongly marked interruptions

in the movements of the internodes I have observed in hardly any

other plant.

The leaves bear four leaflets, themselves subdivided, and terminate

in much-branched tendrils. The main petiole of the leaf, whilst

young, moves spontaneously, and follows nearly the same irregular

course and at about the same rate as the internodes. The movement to

and from the stem is the most conspicuous, and I have seen the chord

of a curved petiole which formed an angle of 59 degrees with the

stem, in an hour afterwards making an angle of 106 degrees. The two

opposite petioles do not move together, and one is sometimes so much

raised as to stand close to the stem, whilst the other is not far

from horizontal. The basal part of the petiole moves less than the

distal part. The tendrils, besides being carried by the moving

petioles and internodes, themselves move spontaneously; and the

opposite tendrils occasionally move in opposite directions. By these

combined movements of the young internodes, petioles, and tendrils, a

considerable space is swept in search of a support.

In young plants the tendrils are about three inches in length: they

bear two lateral and two terminal branches; and each branch

bifurcates twice, with the tips terminating in blunt double hooks,

having both points directed to the same side. All the branches are

sensitive on all sides; and after being lightly rubbed, or after

coming into contact with a stick, bend in about 10 m. One which had

become curved in 10 m. after a light rub, continued bending for

between 3 hrs. and 4 hrs., and became straight again in 8 hrs. or 9

hrs. Tendrils, which have caught nothing, ultimately contract into

an irregular spire, as they likewise do, only much more quickly,

after clasping a support. In both cases the main petiole bearing the

leaflets, which is at first straight and inclined a little upwards,

moves downwards, with the middle part bent abruptly into a right

angle; but this is seen in E. miniatus more plainly than in E.

scaber. The tendrils in this genus act in some respects like those

of Bignonia capreolata; but the whole does not move from the light,

nor do the hooked tips become enlarged into cellular discs. After

the tendrils have come into contact with a moderately thick

cylindrical stick or with rugged bark, the several branches may be

seen slowly to lift themselves up, change their positions, and again

come into contact with the supporting surface. The object of these

movements is to bring the double-hooks at the extremities of the

branches, which naturally face in all directions, into contact with

the wood. I have watched a tendril, half of which had bent itself at

right angles round the sharp corner of a square post, neatly bring

every single hook into contact with both rectangular surfaces. The

appearance suggested the belief, that though the whole tendril is not

sensitive to light, yet that the tips are so, and that they turn and

twist themselves towards any dark surface. Ultimately the branches

arrange themselves very neatly to all the irregularities of the most

rugged bark, so that they resemble in their irregular course a river

with its branches, as engraved on a map. But when a tendril has

wound round a rather thick stick, the subsequent spiral contraction

generally draws it away and spoils the neat arrangement. So it is,

but not in quite so marked a manner, when a tendril has spread itself

over a large, nearly flat surface of rugged bark. We may therefore

conclude that these tendrils are not perfectly adapted to seize

moderately thick sticks or rugged bark. If a thin stick or twig is

placed near a tendril, the terminal branches wind quite round it, and

then seize their own lower branches or the main stem. The stick is

thus firmly, but not neatly, grasped. What the tendrils are really

adapted for, appears to be such objects as the thin culms of certain

grasses, or the long flexible bristles of a brush, or thin rigid

leaves such as those of the Asparagus, all of which they seize in an

admirable manner. This is due to the extremities of the branches

close to the little hooks being extremely sensitive to a touch from

the thinnest object, which they consequently curl round and clasp.

When a small brush, for instance, was placed near a tendril, the tips

of each sub-branch seized one, two, or three of the bristles; and

then the spiral contraction of the several branches brought all these

little parcels close together, so that thirty or forty bristles were

drawn into a single bundle, which afforded an excellent support.

POLEMONIACEAE.--Cobaea scandens.--This is an excellently constructed

climber. The tendrils on a fine plant were eleven inches long, with

the petiole bearing two pairs of leaflets, only two and a half inches

in length. They revolve more rapidly and vigorously than those of

any other tendril-bearer observed by me, with the exception of one

kind of Passiflora. Three large, nearly circular sweeps, directed

against the sun were completed, each in 1 hr. 15 m.; and two other

circles in 1 hr. 20 m. and 1 hr. 23 m. Sometimes a tendril travels

in a much inclined position, and sometimes nearly upright. The lower

part moves but little and the petiole not at all; nor do the

internodes revolve; so that here we have the tendril alone moving.

On the other hand, with most of the species of Bignonia and the

Eccremocarpus, the internodes, tendrils, and petioles all revolved.

The long, straight, tapering main stem of the tendril of the Cobaea

bears alternate branches; and each branch is several times divided,

with the finer branches as thin as very thin bristles and extremely

flexible, so that they are blown about by a breath of air; yet they

are strong and highly elastic. The extremity of each branch is a

little flattened, and terminates in a minute double (though sometimes

single) hook, formed of a hard, translucent, woody substance, and as

sharp as the finest needle. On a tendril which was eleven inches

long I counted ninety-four of these beautifully constructed little

hooks. They readily catch soft wood, or gloves, or the skin of the

naked hand. With the exception of these hardened hooks, and of the

basal part of the central stem, every part of every branchlet is

highly sensitive on all sides to a slight touch, and bends in a few

minutes towards the touched side. By lightly rubbing several sub-

branches on opposite sides, the whole tendril rapidly assumed an

extraordinarily crooked shape. These movements from contact do not

interfere with the ordinary revolving movement. The branches, after

becoming greatly curved from being touched, straighten themselves at

a quicker rate than in almost any other tendril seen by me, namely,

in between half an hour and an hour. After the tendril has caught

any object, spiral contraction likewise begins after an unusually

short interval of time, namely, in about twelve hours.

Before the tendril is mature, the terminal branchlets cohere, and the

hooks are curled closely inwards. At this period no part is

sensitive to a touch; but as soon as the branches diverge and the

hooks stand out, full sensitiveness is acquired. It is a singular

circumstance that immature tendrils revolve at their full velocity

before they become sensitive, but in a useless manner, as in this

state they can catch nothing. This want of perfect co-adaptation,

though only for a short time, between the structure and the functions

of a climbing-plant is a rare event. A tendril, as soon as it is

ready to act, stands, together with the supporting petiole,

vertically upwards. The leaflets borne by the petiole are at this

time quite small, and the extremity of the growing stem is bent to

one side so as to be out of the way of the revolving tendril, which

sweeps large circles directly over head. The tendrils thus revolve

in a position well adapted for catching objects standing above; and

by this means the ascent of the plant is favoured. If no object is

caught, the leaf with its tendril bends downwards and ultimately

assumes a horizontal position. An open space is thus left for the

next succeeding and younger tendril to stand vertically upwards and

to revolve freely. As soon as an old tendril bends downwards, it

loses all power of movement, and contracts spirally into an entangled

mass. Although the tendrils revolve with unusual rapidity, the

movement lasts for only a short time. In a plant placed in the hot-

house and growing vigorously, a tendril revolved for not longer than

36 hours, counting from the period when it first became sensitive;

but during this period it probably made at least 27 revolutions.

When a revolving tendril strikes against a stick, the branches

quickly bend round and clasp it. The little hooks here play an

important part, as they prevent the branches from being dragged away

by the rapid revolving movement, before they have had time to clasp

the stick securely. This is especially the case when only the

extremity of a branch has caught hold of a support. As soon as a

tendril has bent a smooth stick or a thick rugged post, or has come

into contact with planed wood (for it can adhere temporarily even to

so smooth a surface as this), the same peculiar movements may be

observed as those described under Bignonia capreolata and

Eccremocarpus. The branches repeatedly lift themselves up and down;

those which have their hooks already directed downwards remaining in

this position and securing the tendril, whilst the others twist about

until they succeed in arranging themselves in conformity with every

irregularity of the surface, and in bringing their hooks into contact

with the wood. The use of the hooks was well shown by giving the

tendrils tubes and slips of glass to catch; for these, though

temporarily seized, were invariably lost, either during the re-

arrangement of the branches or ultimately when spiral contraction

ensued.

The perfect manner in which the branches arranged themselves,

creeping like rootlets over every inequality of the surface and into

any deep crevice, is a pretty sight; for it is perhaps more

effectually performed by this than by any other species. The action

is certainly more conspicuous, as the upper surfaces of the main

stem, as well as of every branch to the extreme hooks, are angular

and green, whilst the lower surfaces are rounded and purple. I was

led to infer, as in former cases, that a less amount of light guided

these movements of the branches of the tendrils. I made many trials

with black and white cards and glass tubes to prove it, but failed

from various causes; yet these trials countenanced the belief. As a

tendril consists of a leaf split into numerous segments, there is

nothing surprising in all the segments turning their upper surfaces

towards the light, as soon as the tendril is caught and the revolving

movement is arrested. But this will not account for the whole

movement, for the segments actually bend or curve to the dark side

besides turning round on their axes so that their upper surfaces may

face the light.

When the Cobaea grows in the open air, the wind must aid the

extremely flexible tendrils in seizing a support, for I found that a

mere breath sufficed to cause the extreme branches to catch hold by

their hooks of twigs, which they could not have reached by the

revolving movement. It might have been thought that a tendril, thus

hooked by the extremity of a single branch, could not have fairly

grasped its support. But several times I watched cases like the

following: tendril caught a thin stick by the hooks of one of its

two extreme branches; though thus held by the tip, it still tried to

revolve, bowing itself to all sides, and by this movement the other

extreme branch soon caught the stick. The first branch then loosed

itself, and, arranging its hooks, again caught hold. After a time,

from the continued movement of the tendril, the hooks of a third

branch caught hold. No other branches, as the tendril then stood,

could possibly have touched the stick. But before long the upper

part of the main stem began to contract into an open spire. It thus

dragged the shoot which bore the tendril towards the stick; and as

the tendril continually tried to revolve, a fourth branch was brought

into contact. And lastly, from the spiral contraction travelling

down both the main stem and the branches, all of them, one after

another, were ultimately brought into contact with the stick. They

then wound themselves round it and round one another, until the whole

tendril was tied together in an inextricable knot. The tendrils,

though at first quite flexible, after having clasped a support for a

time, become more rigid and stronger than they were at first. Thus

the plant is secured to its support in a perfect manner.

LEGUMINOSAE.--Pisum sativum.--The common pea was the subject of a

valuable memoir by Dutrochet, {27} who discovered that the internodes

and tendrils revolve in ellipses. The ellipses are generally very

narrow, but sometimes approach to circles. I several times observed

that the longer axis slowly changed its direction, which is of

importance, as the tendril thus sweeps a wider space. Owing to this

change of direction, and likewise to the movement of the stem towards

the light, the successive irregular ellipses generally form an

irregular spire. I have thought it worth while to annex a tracing of

the course pursued by the upper internode (the movement of the

tendril being neglected) of a young plant from 8.40 A.M. to 9.15 P.M.

The course was traced on a hemispherical glass placed over the plant,

and the dots with figures give the hours of observation; each dot

being joined by a straight line. No doubt all the lines would have

been curvilinear if the course had been observed at much shorter

intervals. The extremity of the petiole, from which the young

tendril arose, was two inches from the glass, so that if a pencil two

inches in length could have been affixed to the petiole, it would

have traced the annexed figure on the under side of the glass; but it

must be remembered that the figure is reduced by one-half.

Neglecting the first great sweep towards the light from the figure 1

to 2, the end of the petiole swept a space 4 inches across in one

direction, and 3 inches in another. As a full-grown tendril is

considerably above two inches in length, and as the tendril itself

bends and revolves in harmony with the internode, a considerably

wider space is swept than is here represented on a reduced scale.

Dutrochet observed the completion of an ellipse in 1 hr. 20 m.; and I

saw one completed in 1 hr. 30 m. The direction followed is variable,

either with or against the sun.

Dutrochet asserts that the petioles of the leaves spontaneously

revolve, as well as the young internodes and tendrils; but he does

not say that he secured the internodes; when this was done, I could

never detect any movement in the petiole, except to and from the

light.

The tendrils, on the other hand, when the internodes and petioles are

secured, describe irregular spires or regular ellipses, exactly like

those made by the internodes. A young tendril, only 1.125 of an inch

in length, revolved. Dutrochet has shown that when a plant is placed

in a room, so that the light enters laterally, the internodes travel

much quicker to the light than from it: on the other hand, he

asserts that the tendril itself moves from the light towards the dark

side of the room. With due deference to this great observer, I think

he was mistaken, owing to his not having secured the internodes. I

took a young plant with highly sensitive tendrils, and tied the

petiole so that the tendril alone could move; it completed a perfect

ellipse in 1 hr. 30 m.; I then turned the plant partly round, but

this made no change in the direction of the succeeding ellipse. The

next day I watched a plant similarly secured until the tendril (which

was highly sensitive) made an ellipse in a line exactly to and from

the light; the movement was so great that the tendril at the two ends

of its elliptical course bent itself a little beneath the horizon,

thus travelling more than 180 degrees; but the curvature was fully as

great towards the light as towards the dark side of the room. I

believe Dutrochet was misled by not having secured the internodes,

and by having observed a plant of which the internodes and tendrils

no longer curved in harmony together, owing to inequality of age.

Dutrochet made no observations on the sensitiveness of the tendrils.

These, whilst young and about an inch in length with the leaflets on

the petiole only partially expanded, are highly sensitive; a single

light touch with a twig on the inferior or concave surface near the

tip caused them to bend quickly, as did occasionally a loop of thread

weighing one-seventh of a grain (9.25 mg.). The upper or convex

surface is barely or not at all sensitive. Tendrils, after bending

from a touch, straighten themselves in about two hours, and are then

ready to act again. As soon as they begin to grow old, the

extremities of their two or three pairs of branches become hooked,

and they then appear to form an excellent grappling instrument; but

this is not the case. For at this period they have generally quite

lost their sensitiveness; and when hooked on to twigs, some were not

at all affected, and others required from 18 hrs. to 24 hrs. before

clasping such twigs; nevertheless, they were able to utilise the last

vestige of irritability owing to their extremities being hooked.

Ultimately the lateral branches contract spirally, but not the middle

or main stem.

Lathyrus aphaca.--This plant is destitute of leaves, except during a

very early age, these being replaced by tendrils, and the leaves

themselves by large stipules. It might therefore have been expected

that the tendrils would have been highly organized, but this is not

so. They are moderately long, thin, and unbranched, with their tips

slightly curved. Whilst young they are sensitive on all sides, but

chiefly on the concave side of the extremity. They have no

spontaneous revolving power, but are at first inclined upwards at an

angle of about 45 degrees, then move into a horizontal position, and

ultimately bend downwards. The young internodes, on the other hand,

revolve in ellipses, and carry with them the tendrils. Two ellipses

were completed, each in nearly 5 hrs.; their longer axes were

directed at about an angle of 45 degrees to the axis of the

previously made ellipse.

Lathyrus grandiflorus.--The plants observed were young and not

growing vigorously, yet sufficiently so, I think, for my observations

to be trusted. If so, we have the rare case of neither internodes

nor tendrils revolving. The tendrils of vigorous plants are above 4

inches in length, and are often twice divided into three branches;

the tips are curved and are sensitive on their concave sides; the

lower part of the central stem is hardly at all sensitive. Hence

this plant appears to climb simply by its tendrils being brought,

through the growth of the stem, or more efficiently by the wind, into

contact with surrounding objects, which they then clasp. I may add

that the tendrils, or the internodes, or both, of Vicia sativa

revolve.

COMPOSITAE.--Mutisia clematis.--The immense family of the Compositae

is well known to include very few climbing plants. We have seen in

the Table in the first chapter that Mikania scandens is a regular

twiner, and F. Muller informs me that in S. Brazil there is another

species which is a leaf-climber. Mutisia is the only genus in the

family, as far as I can learn, which bears tendrils: it is therefore

interesting to find that these, though rather less metamorphosed from

their primordial foliar condition than are most other tendrils, yet

display all the ordinary characteristic movements, both those that

are spontaneous and those which are excited by contact.

The long leaf bears seven or eight alternate leaflets, and terminates

in a tendril which, in a plant of considerable size, was 5 inches in

length. It consists generally of three branches; and these, although

much elongated, evidently represent the petioles and midribs of three

leaflets; for they closely resemble the same parts in an ordinary

leaf, in being rectangular on the upper surface, furrowed, and edged

with green. Moreover, the green edging of the tendrils of young

plants sometimes expands into a narrow lamina or blade. Each branch

is curved a little downwards, and is slightly hooked at the

extremity.

A young upper internode revolved, judging from three revolutions, at

an average rate of 1 hr. 38 m.; it swept ellipses with the longer

axes directed at right angles to one another; but the plant,

apparently, cannot twine. The petioles and the tendrils are both in

constant movement. But their movement is slower and much less

regularly elliptical than that of the internodes. They appear to be

much affected by the light, for the whole leaf usually sinks down

during the night and rises during the day, moving, also, during the

day in a crooked course to the west. The tip of the tendril is

highly sensitive on the lower surface; and one which was just touched

with a twig became perceptibly curved in 3 m., and another in 5 m.;

the upper surface is not at all sensitive; the sides are moderately

sensitive, so that two branches which were rubbed on their inner

sides converged and crossed each other. The petiole of the leaf and

the lower parts of the tendril, halfway between the upper leaflet and

the lowest branch, are not sensitive. A tendril after curling from a

touch became straight again in about 6 hrs., and was ready to re-act;

but one that had been so roughly rubbed as to have coiled into a

helix did not become perfectly straight until after 13 hrs. The

tendrils retain their sensibility to an unusually late age; for one

borne by a leaf with five or six fully developed leaves above, was

still active. If a tendril catches nothing, after a considerable

interval of time the tips of the branches curl a little inwards; but

if it clasps some object, the whole contracts spirally.

SMILACEAE.--Smilax aspera, var. maculata.--Aug. St.-Hilaire {28}

considers that the tendrils, which rise in pairs from the petiole,

are modified lateral leaflets; but Mohl (p. 41) ranks them as

modified stipules. These tendrils are from 1.5 to 1.75 inches in

length, are thin, and have slightly curved, pointed extremities.

They diverge a little from each other, and stand at first nearly

upright. When lightly rubbed on either side, they slowly bend to

that side, and subsequently become straight again. The back or

convex side when placed in contact with a stick became just

perceptibly curved in 1 hr. 20 m., but did not completely surround it

until 48 hrs. had elapsed; the concave side of another became

considerably curved in 2 hrs. and clasped a stick in 5 hrs. As the

pairs of tendrils grow old, one tendril diverges more and more from

the other, and both slowly bend backwards and downwards, so that

after a time they project on the opposite side of the stem to that

from which they arise. They then still retain their sensitiveness,

and can clasp a support placed BEHIND the stem. Owing to this power,

the plant is able to ascend a thin upright stick. Ultimately the two

tendrils belonging to the same petiole, if they do not come into

contact with any object, loosely cross each other behind the stem, as

at B, in fig. 7. This movement of the tendrils towards and round the

stem is, to a certain extent, guided by their avoidance of the light;

for when a plant stood so that one of the two tendrils was compelled

in thus slowly moving to travel towards the light, and the other from

the light, the latter always moved, as I repeatedly observed, more

quickly than its fellow. The tendrils do not contract spirally in

any case. Their chance of finding a support depends on the growth of

the plant, on the wind, and on their own slow backward and downward

movement, which, as we have just seen, is guided, to a certain

extent, by the avoidance of the light; for neither the internodes nor

the tendrils have any proper revolving movement. From this latter

circumstance, from the slow movements of the tendrils after contact

(though their sensitiveness is retained for an unusual length of

time), from their simple structure and shortness, this plant is a

less perfect climber than any other tendril-bearing species observed

by me. The plant whilst young and only a few inches in height, does

not produce any tendrils; and considering that it grows to only about

8 feet in height, that the stem is zigzag and is furnished, as well

as the petioles, with spines, it is surprising that it should be

provided with tendrils, comparatively inefficient though these are.

The plant might have been left, one would have thought, to climb by

the aid of its spines alone, like our brambles. As, however, it

belongs to a genus, some of the species of which are furnished with

much longer tendrils, we may suspect that it possesses these organs

solely from being descended from progenitors more highly organized in

this respect.

FUMARIACEAE.--Corydalis claviculata.--According to Mohl (p. 43), the

extremities of the branched stem, as well as the leaves, are

converted into tendrils. In the specimens examined by me all the

tendrils were certainly foliar, and it is hardly credible that the

same plant should produce tendrils of a widely different homological

nature. Nevertheless, from this statement by Mohl, I have ranked

this species amongst the tendril-bearers; if classed exclusively by

its foliar tendrils, it would be doubtful whether it ought not to

have been placed amongst the leaf-climbers, with its allies, Fumaria

and Adlumia. A large majority of its so-called tendrils still bear

leaflets, though excessively reduced in size; but some few of them

may properly be designated as tendrils, for they are completely

destitute of laminae or blades. Consequently, we here behold a plant

in an actual state of transition from a leaf-climber to a tendril-

bearer. Whilst the plant is rather young, only the outer leaves, but

when full-grown all the leaves, have their extremities converted into

more or less perfect tendrils. I have examined specimens from one

locality alone, viz. Hampshire; and it is not improbable that plants

growing under different conditions might have their leaves a little

more or less changed into true tendrils.

Whilst the plant is quite young, the first-formed leaves are not

modified in any way, but those next formed have their terminal

leaflets reduced in size, and soon all the leaves assume the

structure represented in the following drawing. This leaf bore nine

leaflets; the lower ones being much subdivided. The terminal portion

of the petiole, about 1.5 inch in length (above the leaflet f), is

thinner and more elongated than the lower part, and may be considered

as the tendril. The leaflets borne by this part are greatly reduced

in size, being, on an average, about the tenth of an inch in length

and very narrow; one small leaflet measured one-twelfth of an inch in

length and one-seventy-fifth in breadth (2.116 mm. and 0.339 mm.), so

that it was almost microscopically minute. All the reduced leaflets

have branching nerves, and terminate in little spines, like those of

the fully developed leaflets. Every gradation could be traced, until

we come to branchlets (as a and d in the figure) which show no

vestige of a lamina or blade. Occasionally all the terminal

branchlets of the petiole are in this condition, and we then have a

true tendril.

The several terminal branches of the petiole bearing the much reduced

leaflets (a, b, c, d) are highly sensitive, for a loop of thread

weighing only the one-sixteenth of a grain (4.05 mg.) caused them to

become greatly curved in under 4 hrs. When the loop was removed, the

petioles straightened themselves in about the same time. The petiole

(e) was rather less sensitive; and in another specimen, in which the

corresponding petiole bore rather larger leaflets, a loop of thread

weighing one-eighth of a grain did not cause curvature until 18 hrs.

had elapsed. Loops of thread weighing one-fourth of a grain, left

suspended on the lower petioles (f to l) during several days,

produced no effect. Yet the three petioles f, g, and h were not

quite insensible, for when left in contact with a stick for a day or

two they slowly curled round it. Thus the sensibility of the petiole

gradually diminishes from the tendril-like extremity to the base.

The internodes of the stem are not at all sensitive, which makes

Mohl's statement that they are sometimes converted into tendrils the

more surprising, not to say improbable.

The whole leaf, whilst young and sensitive, stands almost vertically

upwards, as we have seen to be the case with many tendrils. It is in

continual movement, and one that I observed swept at an average rate

of about 2 hrs. for each revolution, large, though irregular,

ellipses, which were sometimes narrow, sometimes broad, with their

longer axes directed to different points of the compass. The young

internodes, likewise revolved irregularly in ellipses or spires; so

that by these combined movements a considerable space was swept for a

support. If the terminal and attenuated portion of a petiole fails

to seize any object, it ultimately bends downwards and inwards, and

soon loses all irritability and power of movement. This bending down

differs much in nature from that which occurs with the extremities of

the young leaves in many species of Clematis; for these, when thus

bent downwards or hooked, first acquire their full degree of

sensitiveness.

Dicentra thalictrifolia.--In this allied plant the metamorphosis of

the terminal leaflets is complete, and they are converted into

perfect tendrils. Whilst the plant is young, the tendrils appear

like modified branches, and a distinguished botanist thought that

they were of this nature; but in a full-grown plant there can be no

doubt, as I am assured by Dr. Hooker, that they are modified leaves.

When of full size, they are above 5 inches in length; they bifurcate

twice, thrice, or even four times; their extremities are hooked and

blunt. All the branches of the tendrils are sensitive on all sides,

but the basal portion of the main stem is only slightly so. The

terminal branches when lightly rubbed with a twig became curved in

the course of from 30 m. to 42 m., and straightened themselves in

between 10 hrs. and 20 hrs. A loop of thread weighing one-eighth of

a grain plainly caused the thinner branches to bend, as did

occasionally a loop weighing one-sixteenth of a grain; but this

latter weight, though left suspended, was not sufficient to cause a

permanent flexure. The whole leaf with its tendril, as well as the

young upper internodes, revolves vigorously and quickly, though

irregularly, and thus sweeps a wide space. The figure traced on a

bell-glass was either an irregular spire or a zigzag line. The

nearest approach to an ellipse was an elongated figure of 8, with one

end a little open, and this was completed in 1 hr. 53 m. During a

period of 6 hrs. 17 m. another shoot made a complex figure,

apparently representing three and a half ellipses. When the lower

part of the petiole bearing the leaflets was securely fastened, the

tendril itself described similar but much smaller figures.

This species climbs well. The tendrils after clasping a stick become

thicker and more rigid; but the blunt hooks do not turn and adapt

themselves to the supporting surface, as is done in so perfect a

manner by some Bignoniaceae and Cobaea. The tendrils of young

plants, two or three feet in height, are only half the length of

those borne by the same plant when grown taller, and they do not

contract spirally after clasping a support, but only become slightly

flexuous. Full-sized tendrils, on the other hand, contract spirally,

with the exception of the thick basal portion. Tendrils which have

caught nothing simply bend downwards and inwards, like the

extremities of the leaves of the Corydalis claviculata. But in all

cases the petiole after a time is angularly and abruptly bent

downwards like that of Eccremocarpus.

CHAPTER IV.--TENDRIL-BEARERS--(continued).

CUCURBITACEAE.--Homologous nature of the tendrils--Echinocystis

lobata, remarkable movements of the tendrils to avoid seizing the

terminal shoot--Tendrils not excited by contact with another tendril

or by drops of water--Undulatory movement of the extremity of the

tendril--Hanburya, adherent discs--VITACAE--Gradation between the

flower-peduncles and tendrils of the vine--Tendrils of the Virginian

Creeper turn from the light, and, after contact, develop adhesive

discs--SAPINDACEAE--PASSIFLORACEAE--Passiflora gracilis--Rapid

revolving movement and sensitiveness of the tendrils--Not sensitive

to the contact of other tendrils or of drops of water--Spiral

contraction of tendrils--Summary on the nature and action of

tendrils.

CUCURBITACEAE.--The tendrils in this family have been ranked by

competent judges as modified leaves, stipules, or branches; or as

partly a leaf and partly a branch. De Candolle believes that the

tendrils differ in their homological nature in two of the tribes.

{29} From facts recently adduced, Mr. Berkeley thinks that Payer's

view is the most probable, namely, that the tendril is "a separate

portion of the leaf itself;" but much may be said in favour of the

belief that it is a modified flower-peduncle. {30}

Echinocystis lobata.--Numerous observations were made on this plant

(raised from seed sent me by Prof. Asa Gray), for the spontaneous

revolving movements of the internodes and tendrils were first

observed by me in this case, and greatly perplexed me. My

observations may now be much condensed. I observed thirty-five

revolutions of the internodes and tendrils; the slowest rate was 2

hrs. and the average rate, with no great fluctuations, 1 hr. 40 m.

Sometimes I tied the internodes, so that the tendrils alone moved; at

other times I cut off the tendrils whilst very young, so that the

internodes revolved by themselves; but the rate was not thus

affected. The course generally pursued was with the sun, but often

in an opposite direction. Sometimes the movement during a short time

would either stop or be reversed; and this apparently was due to

interference from the light, as, for instance, when I placed a plant

close to a window. In one instance, an old tendril, which had nearly

ceased revolving, moved in one direction, whilst a young tendril

above moved in an opposite course. The two uppermost internodes

alone revolve; and as soon as the lower one grows old, only its upper

part continues to move. The ellipses or circles swept by the summits

of the internodes are about three inches in diameter; whilst those

swept by the tips of the tendrils, are from 15 to 16 inches in

diameter. During the revolving movement, the internodes become

successively curved to all points of the compass; in one part of

their course they are often inclined, together with the tendrils, at

about 45 degrees to the horizon, and in another part stand vertically

up. There was something in the appearance of the revolving

internodes which continually gave the false impression that their

movement was due to the weight of the long and spontaneously

revolving tendril; but, on cutting off the latter with sharp

scissors, the top of the shoot rose only a little, and went on

revolving. This false appearance is apparently due to the internodes

and tendrils all curving and moving harmoniously together.

A revolving tendril, though inclined during the greater part of its

course at an angle of about 45 degrees (in one case of only 37

degrees) above the horizon, stiffened and straightened itself from

tip to base in a certain part of its course, thus becoming nearly or

quite vertical. I witnessed this repeatedly; and it occurred both

when the supporting internodes were free and when they were tied up;

but was perhaps most conspicuous in the latter case, or when the

whole shoot happened to be much inclined. The tendril forms a very

acute angle with the projecting extremity of the stem or shoot; and

the stiffening always occurred as the tendril approached, and had to

pass over the shoot in its circular course. If it had not possessed

and exercised this curious power, it would infallibly have struck

against the extremity of the shoot and been arrested. As soon as the

tendril with its three branches begins to stiffen itself in this

manner and to rise from an inclined into a vertical position, the

revolving motion becomes more rapid; and as soon as the tendril has

succeeded in passing over the extremity of the shoot or point of

difficulty, its motion, coinciding with that from its weight, often

causes it to fall into its previously inclined position so quickly,

that the apex could be seen travelling like the minute hand of a

gigantic clock.

The tendrils are thin, from 7 to 9 inches in length, with a pair of

short lateral branches rising not far from the base. The tip is

slightly and permanently curved, so as to act to a limited extent as

a hook. The concave side of the tip is highly sensitive to a touch;

but not so the convex side, as was likewise observed to be the case

with other species of the family by Mohl (p. 65). I repeatedly

proved this difference by lightly rubbing four or five times the

convex side of one tendril, and only once or twice the concave side

of another tendril, and the latter alone curled inwards. In a few

hours afterwards, when the tendrils which had been rubbed on the

concave side had straightened themselves, I reversed the process of

rubbing, and always with the same result. After touching the concave

side, the tip becomes sensibly curved in one or two minutes; and

subsequently, if the touch has been at all rough, it coils itself

into a helix. But the helix will, after a time, straighten itself,

and be again ready to act. A loop of thin thread only one-sixteenth

of a grain in weight caused a temporary flexure. The lower part was

repeatedly rubbed rather roughly, but no curvature ensued; yet this

part is sensitive to prolonged pressure, for when it came into

contact with a stick, it would slowly wind round it.

One of my plants bore two shoots near together, and the tendrils were

repeatedly drawn across one another, but it is a singular fact that

they did not once catch each other. It would appear as if they had

become habituated to contact of this kind, for the pressure thus

caused must have been much greater than that caused by a loop of soft

thread weighing only the one-sixteenth of a grain. I have, however,

seen several tendrils of Bryonia dioica interlocked, but they

subsequently released one another. The tendrils of the Echinocystis

are also habituated to drops of water or to rain; for artificial rain

made by violently flirting a wet brush over them produced not the

least effect.

The revolving movement of a tendril is not stopped by the curving of

its extremity after it has been touched. When one of the lateral

branches has firmly clasped an object, the middle branch continues to

revolve. When a stem is bent down and secured, so that the tendril

depends but is left free to move, its previous revolving movement is

nearly or quite stopped; but it soon begins to bend upwards, and as

soon as it has become horizontal the revolving movement recommences.

I tried this four times; the tendril generally rose to a horizontal

position in an hour or an hour and a half; but in one case, in which

a tendril depended at an angle of 45 degrees beneath the horizon, the

uprising took two hours; in half an hour afterwards it rose to 23

degrees above the horizon and then recommenced revolving. This

upward movement is independent of the action of light, for it

occurred twice in the dark, and on another occasion the light came in

on one side alone. The movement no doubt is guided by opposition to

the force of gravity, as in the case of the ascent of the plumules of

germinating seeds.

A tendril does not long retain its revolving power; and as soon as

this is lost, it bends downwards and contracts spirally. After the

revolving movement has ceased, the tip still retains for a short time

its sensitiveness to contact, but this can be of little or no use to

the plant.

Though the tendril is highly flexible, and though the extremity

travels, under favourable circumstances, at about the rate of an inch

in two minutes and a quarter, yet its sensitiveness to contact is so

great that it hardly ever fails to seize a thin stick placed in its

path. The following case surprised me much: I placed a thin,

smooth, cylindrical stick (and I repeated the experiment seven times)

so far from a tendril, that its extremity could only curl half or

three-quarters round the stick; but I always found that the tip

managed in the course of a few hours to curl twice or even thrice

round the stick. I at first thought that this was due to rapid

growth on the outside; but by coloured points and measurements I

proved that there had been no sensible increase of length within the

time. When a stick, flat on one side, was similarly placed, the tip

of the tendril could not curl beyond the flat surface, but coiled

itself into a helix, which, turning to one side, lay flat on the

little flat surface of wood. In one instance a portion of tendril

three-quarters of an inch in length was thus dragged on to the flat

surface by the coiling in of the helix. But the tendril thus

acquires a very insecure hold, and generally after a time slips off.

In one case alone the helix subsequently uncoiled itself, and the tip

then passed round and clasped the stick. The formation of the helix

on the flat side of the stick apparently shows us that the continued

striving of the tip to curl itself closely inwards gives the force

which drags the tendril round a smooth cylindrical stick. In this

latter case, whilst the tendril was slowly and quite insensibly

crawling onwards, I observed several times through a lens that the

whole surface was not in close contact with the stick; and I can

understand the onward progress only by supposing that the movement is

slightly undulatory or vermicular, and that the tip alternately

straightens itself a little and then again curls inwards. It thus

drags itself onwards by an insensibly slow, alternate movement, which

may be compared to that of a strong man suspended by the ends of his

fingers to a horizontal pole, who works his fingers onwards until he

can grasp the pole with the palm of his hand. However this may be,

the fact is certain that a tendril which has caught a round stick

with its extreme point, can work itself onwards until it has passed

twice or even thrice round the stick, and has permanently grasped it.

Hanburya Mexicana.--The young internodes and tendrils of this

anomalous member of the family, revolve in the same manner and at

about the same rate as those of the Echinocystis. The stem does not

twine, but can ascend an upright stick by the aid of its tendrils.

The concave tip of the tendril is very sensitive; after it had become

rapidly coiled into a ring owing to a single touch, it straightened

itself in 50 m. The tendril, when in full action, stands vertically

up, with the projecting extremity of the young stem thrown a little

on one side, so as to be out of the way; but the tendril bears on the

inner side, near its base, a short rigid branch, which projects out

at right angles like a spur, with the terminal half bowed a little

downwards. Hence, as the main vertical branch revolves, the spur,

from its position and rigidity, cannot pass over the extremity of the

shoot, in the same curious manner as do the three branches of the

tendril of the Echinocystis, namely, by stiffening themselves at the

proper point. The spur is therefore pressed laterally against the

young stem in one part of the revolving course, and thus the sweep of

the lower part of the main branch is much restricted. A nice case of

co-adaptation here comes into play: in all the other tendrils

observed by me, the several branches become sensitive at the same

period: had this been the case with the Hanburya, the inwardly

directed, spur-like branch, from being pressed, during the revolving

movement, against the projecting end of the shoot, would infallibly

have seized it in a useless or injurious manner. But the main branch

of the tendril, after revolving for a time in a vertical position,

spontaneously bends downwards; and in doing so, raises the spur-like

branch, which itself also curves upwards; so that by these combined

movements it rises above the projecting end of the shoot, and can now

move freely without touching the shoot; and now it first becomes

sensitive.

The tips of both branches, when they come into contact with a stick,

grasp it like any ordinary tendril. But in the course of a few days,

the lower surface swells and becomes developed into a cellular layer,

which adapts itself closely to the wood, and firmly adheres to it.

This layer is analogous to the adhesive discs formed by the

extremities of the tendrils of some species of Bignonia and of

Ampelopsis; but in the Hanburya the layer is developed along the

terminal inner surface, sometimes for a length of 1.75 inches, and

not at the extreme tip. The layer is white, whilst the tendril is

green, and near the tip it is sometimes thicker than the tendril

itself; it generally spreads a little beyond the sides of the

tendril, and is fringed with free elongated cells, which have

enlarged globular or retort-shaped heads. This cellular layer

apparently secretes some resinous cement; for its adhesion to the

wood was not lessened by an immersion of 24 hrs. in alcohol or water,

but was quite loosened by a similar immersion in ether or turpentine.

After a tendril has once firmly coiled itself round a stick, it is

difficult to imagine of what use the adhesive cellular layer can be.

Owing to the spiral contraction which soon ensues, the tendrils were

never able to remain, excepting in one instance, in contact with a

thick post or a nearly flat surface; if they had quickly become

attached by means of the adhesive layer, this would evidently have

been of service to the plant.

The tendrils of Bryonia dioica, Cucurbita ovifera, and Cucumis sativa

are sensitive and revolve. Whether the internodes likewise revolve I

did not observe. In Anguria Warscewiczii, the internodes, though

thick and stiff, revolve: in this plant the lower surface of the

tendril, some time after clasping a stick, produces a coarsely

cellular layer or cushion, which adapts itself closely to the wood,

like that formed by the tendril of the Hanburya; but it is not in the

least adhesive. In Zanonia Indica, which belongs to a different

tribe of the family, the forked tendrils and the internodes revolve

in periods between 2 hrs. 8 m. and 3 hrs. 35 m., moving against the

sun.

VITACEAE.--In this family and in the two following, namely, the

Sapindaceae and Passifloraceae, the tendrils are modified flower-

peduncles; and are therefore axial in their nature. In this respect

they differ from all those previously described, with the exception,

perhaps, of the Cucurbitaceae. The homological nature, however, of a

tendril seems to make no difference in its action.

Vitis vinifera.--The tendril is thick and of great length; one from a

vine growing out of doors and not vigorously, was 16 inches long. It

consists of a peduncle (A), bearing two branches which diverge

equally from it. One of the branches (B) has a scale at its base; it

is always, as far as I have seen, longer than the other and often

bifurcates. The branches when rubbed become curved, and subsequently

straighten themselves. After a tendril has clasped any object with

its extremity, it contracts spirally; but this does not occur (Palm,

p. 56) when no object has been seized. The tendrils move

spontaneously from side to side; and on a very hot day, one made two

elliptical revolutions, at an average rate of 2 hrs. 15 m. During

these movements a coloured line, painted along the convex surface,

appeared after a time on one side, then on the concave side, then on

the opposite side, and lastly again on the convex side. The two

branches of the same tendril have independent movements. After a

tendril has spontaneously revolved for a time, it bends from the

light towards the dark: I do not state this on my own authority, but

on that of Mohl and Dutrochet. Mohl (p. 77) says that in a vine

planted against a wall the tendrils point towards it, and in a

vineyard generally more or less to the north.

The young internodes revolve spontaneously; but the movement is

unusually slight. A shoot faced a window, and I traced its course on

the glass during two perfectly calm and hot days. On one of these

days it described, in the course of ten hours, a spire, representing

two and a half ellipses. I also placed a bell-glass over a young

Muscat grape in the hot-house, and it made each day three or four

very small oval revolutions; the shoot moving less than half an inch

from side to side. Had it not made at least three revolutions whilst

the sky was uniformly overcast, I should have attributed this slight

degree of movement to the varying action of the light. The extremity

of the stem is more or less bent downwards, but it never reverses its

curvature, as so generally occurs with twining plants.

Various authors (Palm, p. 55; Mohl, p. 45; Lindley, &c.) believe that

the tendrils of the vine are modified flower-peduncles. I here give

a drawing (fig. 10) of the ordinary state of a young flower-stalk:

it consists of the "common peduncle" (A); of the "flower-tendril"

(B), which is represented as having caught a twig; and of the "sub-

peduncle" (C) bearing the flower-buds. The whole moves

spontaneously, like a true tendril, but in a less degree; the

movement, however, is greater when the sub-peduncle (C) does not bear

many flower-buds. The common peduncle (A) has not the power of

clasping a support, nor has the corresponding part of a true tendril.

The flower-tendril (B) is always longer than the sub-peduncle (C) and

has a scale at its base; it sometimes bifurcates, and therefore

corresponds in every detail with the longer scale-bearing branch (B,

fig. 9) of the true tendril. It is, however, inclined backwards

from the sub-peduncle (C), or stands at right angles with it, and is

thus adapted to aid in carrying the future bunch of grapes. When

rubbed, it curves and subsequently straightens itself; and it can, as

is shown in the drawing, securely clasp a support. I have seen an

object as soft as a young vine-leaf caught by one.

The lower and naked part of the sub-peduncle (C) is likewise slightly

sensitive to a rub, and I have seen it bent round a stick and even

partly round a leaf with which it had come into contact. That the

sub-peduncle has the same nature as the corresponding branch of an

ordinary tendril, is well shown when it bears only a few flowers; for

in this case it becomes less branched, increases in length, and gains

both in sensitiveness and in the power of spontaneous movement. I

have twice seen sub-peduncles which bore from thirty to forty flower-

buds, and which had become considerably elongated and were completely

wound round sticks, exactly like true tendrils. The whole length of

another sub-peduncle, bearing only eleven flower-buds, quickly became

curved when slightly rubbed; but even this scanty number of flowers

rendered the stalk less sensitive than the other branch, that is, the

flower-tendril; for the latter after a lighter rub became curved more

quickly and in a greater degree. I have seen a sub-peduncle thickly

covered with flower-buds, with one of its higher lateral branchlets

bearing from some cause only two buds; and this one branchlet had

become much elongated and had spontaneously caught hold of an

adjoining twig; in fact, it formed a little sub-tendril. The

increasing length of the sub-peduncle (C) with the decreasing number

of the flower-buds is a good instance of the law of compensation. In

accordance with this same principle, the true tendril as a whole is

always longer than the flower-stalk; for instance, on the same plant,

the longest flower-stalk (measured from the base of the common

peduncle to the tip of the flower-tendril) was 8.5 inches in length,

whilst the longest tendril was nearly double this length, namely 16

inches.

The gradations from the ordinary state of a flower-stalk, as

represented in the drawing (fig. 10), to that of a true tendril (fig.

9) are complete. We have seen that the sub-peduncle (C), whilst

still bearing from thirty to forty flower-buds, sometimes becomes a

little elongated and partially assumes all the characters of the

corresponding branch of a true tendril. From this state we can trace

every stage till we come to a full-sized perfect tendril, bearing on

the branch which corresponds with the sub-peduncle one single flower-

bud! Hence there can be no doubt that the tendril is a modified

flower-peduncle.

Another kind of gradation well deserves notice. Flower-tendrils (B,

fig. 10) sometimes produce a few flower-buds. For instance, on a

vine growing against my house, there were thirteen and twenty-two

flower-buds respectively on two flower-tendrils, which still retained

their characteristic qualities of sensitiveness and spontaneous

movement, but in a somewhat lessened degree. On vines in hothouses,

so many flowers are occasionally produced on the flower-tendrils that

a double bunch of grapes is the result; and this is technically

called by gardeners a "cluster." In this state the whole bunch of

flowers presents scarcely any resemblance to a tendril; and, judging

from the facts already given, it would probably possess little power

of clasping a support, or of spontaneous movement. Such flower-

stalks closely resemble in structure those borne by Cissus. This

genus, belonging to the same family of the Vitaceae, produces well-

developed tendrils and ordinary bunches of flowers; but there are no

gradations between the two states. If the genus Vitis had been

unknown, the boldest believer in the modification of species would

never have surmised that the same individual plant, at the same

period of growth, would have yielded every possible gradation between

ordinary flower-stalks for the support of the flowers and fruit, and

tendrils used exclusively for climbing. But the vine clearly gives

us such a case; and it seems to me as striking and curious an

instance of transition as can well be conceived.

Cissus discolor.--The young shoots show no more movement than can be

accounted for by daily variations in the action of the light. The

tendrils, however, revolve with much regularity, following the sun;

and, in the plants observed by me, swept circles of about 5 inches in

diameter. Five circles were completed in the following times:- 4

hrs. 45 m., 4 hrs. 50 m., 4 hrs. 45 m., 4 hrs. 30 m., and 5 hrs. The

same tendril continues to revolve during three or four days. The

tendrils are from 3.5 to 5 inches in length. They are formed of a

long foot-stalk, bearing two short branches, which in old plants

again bifurcate. The two branches are not of quite equal length; and

as with the vine, the longer one has a scale at its base. The

tendril stands vertically upwards; the extremity of the shoot being

bent abruptly downwards, and this position is probably of service to

the plant by allowing the tendril to revolve freely and vertically.

Both branches of the tendril, whilst young, are highly sensitive. A

touch with a pencil, so gentle as only just to move a tendril borne

at the end of a long flexible shoot, sufficed to cause it to become

perceptibly curved in four or five minutes. It became straight again

in rather above one hour. A loop of soft thread weighing one-seventh

of a grain (9.25 mg.) was thrice tried, and each time caused the

tendril to become curved in 30 or 40 m. Half this weight produced no

effect. The long foot-stalk is much less sensitive, for a slight

rubbing produced no effect, although prolonged contact with a stick

caused it to bend. The two branches are sensitive on all sides, so

that they converge if touched on their inner sides, and diverge if

touched on their outer sides. If a branch be touched at the same

time with equal force on opposite sides, both sides are equally

stimulated and there is no movement. Before examining this plant, I

had observed only tendrils which are sensitive on one side alone, and

these when lightly pressed between the finger and thumb become

curved; but on thus pinching many times the tendrils of the Cissus no

curvature ensued, and I falsely inferred at first that they were not

at all sensitive.

Cissus antarcticus.--The tendrils on a young plant were thick and

straight, with the tips a little curved. When their concave surfaces

were rubbed, and it was necessary to do this with some force, they

very slowly became curved, and subsequently straight again. They are

therefore much less sensitive than those of the last species; but

they made two revolutions, following the sun, rather more rapidly,

viz., in 3 hrs. 30 m. and 4 hrs. The internodes do not revolve.

Ampelopsis hederacea (Virginian Creeper).--The internodes apparently

do not move more than can be accounted for by the varying action of

the light. The tendrils are from 4 to 5 inches in length, with the

main stem sending off several lateral branches, which have their tips

curved, as may be seen in the upper figure (fig. 11). They exhibit

no true spontaneous revolving movement, but turn, as was long ago

observed by Andrew Knight, {31} from the light to the dark. I have

seen several tendrils move in less than 24 hours, through an angle of

180 degrees to the dark side of a case in which a plant was placed,

but the movement is sometimes much slower. The several lateral

branches often move independently of one another, and sometimes

irregularly, without any apparent cause. These tendrils are less

sensitive to a touch than any others observed by me. By gentle but

repeated rubbing with a twig, the lateral branches, but not the main

stem, became in the course of three or four hours slightly curved;

but they seemed to have hardly any power of again straightening

themselves. The tendrils of a plant which had crawled over a large

box-tree clasped several of the branches; but I have repeatedly seen

that they will withdraw themselves after seizing a stick. When they

meet with a flat surface of wood or a wall (and this is evidently

what they are adapted for), they turn all their branches towards it,

and, spreading them widely apart, bring their hooked tips laterally

into contact with it. In effecting this, the several branches, after

touching the surface, often rise up, place themselves in a new

position, and again come down into contact with it.

In the course of about two days after a tendril has arranged its

branches so as to press on any surface, the curved tips swell, become

bright red, and form on their under-sides the well-known little discs

or cushions with which they adhere firmly. In one case the tips were

slightly swollen in 38 hrs. after coming into contact with a brick;

in another case they were considerably swollen in 48 hrs., and in an

additional 24 hrs. were firmly attached to a smooth board; and

lastly, the tips of a younger tendril not only swelled but became

attached to a stuccoed wall in 42 hrs. These adhesive discs

resemble, except in colour and in being larger, those of Bignonia

capreolata. When they were developed in contact with a ball of tow,

the fibres were separately enveloped, but not in so effective a

manner as by B. capreolata. Discs are never developed, as far as I

have seen, without the stimulus of at least temporary contact with

some object. {32} They are generally first formed on one side of the

curved tip, the whole of which often becomes so much changed in

appearance, that a line of the original green tissue can be traced

only along the concave surface. When, however, a tendril has clasped

a cylindrical stick, an irregular rim or disc is sometimes formed

along the inner surface at some little distance from the curved tip;

this was also observed (p. 71) by Mohl. The discs consist of

enlarged cells, with smooth projecting hemispherical surfaces,

coloured red; they are at first gorged with fluid (see section given

by Mohl, p. 70), but ultimately become woody.

As the discs soon adhere firmly to such smooth surfaces as planed or

painted wood, or to the polished leaf of the ivy, this alone renders

it probable that some cement is secreted, as has been asserted to be

the case (quoted by Mohl, p. 71) by Malpighi. I removed a number of

discs formed during the previous year from a stuccoed wall, and left

them during many hours, in warm water, diluted acetic acid and

alcohol; but the attached grains of silex were not loosened.

Immersion in sulphuric ether for 24 hrs. loosened them much, but

warmed essential oils (I tried oil of thyme and peppermint)

completely released every particle of stone in the course of a few

hours. This seems to prove that some resinous cement is secreted.

The quantity, however, must be small; for when a plant ascended a

thinly whitewashed wall, the discs adhered firmly to the whitewash;

but as the cement never penetrated the thin layer, they were easily

withdrawn, together with little scales of the whitewash. It must not

be supposed that the attachment is effected exclusively by the

cement; for the cellular outgrowth completely envelopes every minute

and irregular projection, and insinuates itself into every crevice.

A tendril which has not become attached to any body, does not

contract spirally; and in course of a week or two shrinks into the

finest thread, withers and drops off. An attached tendril, on the

other hand, contracts spirally, and thus becomes highly elastic, so

that when the main foot-stalk is pulled the strain is distributed

equally between all the attached discs. For a few days after the

attachment of the discs, the tendril remains weak and brittle, but it

rapidly increases in thickness and acquires great strength. During

the following winter it ceases to live, but adheres firmly in a dead

state both to its own stem and to the surface of attachment. In the

accompanying diagram (fig. 11.) we see the difference between a

tendril (B) some weeks after its attachment to a wall, with one (A)

from the same plant fully grown but unattached. That the change in

the nature of the tissues, as well as the spiral contraction, are

consequent on the formation of the discs, is well shown by any

lateral branches which have not become attached; for these in a week

or two wither and drop off, in the same manner as does the whole

tendril if unattached. The gain in strength and durability in a

tendril after its attachment is something wonderful. There are

tendrils now adhering to my house which are still strong, and have

been exposed to the weather in a dead state for fourteen or fifteen

years. One single lateral branchlet of a tendril, estimated to be at

least ten years old, was still elastic and supported a weight of

exactly two pounds. The whole tendril had five disc-bearing branches

of equal thickness and apparently of equal strength; so that after

having been exposed during ten years to the weather, it would

probably have resisted a strain of ten pounds!

SAPINDACEAE.--Cardiospermum halicacabum.--In this family, as in the

last, the tendrils are modified flower-peduncles. In the present

plant the two lateral branches of the main flower-peduncle have been

converted into a pair of tendrils, corresponding with the single

"flower-tendril" of the common vine. The main peduncle is thin,

stiff, and from 3 to 4.5 inches in length. Near the summit, above

two little bracts, it divides into three branches. The middle one

divides and re-divides, and bears the flowers; ultimately it grows

half as long again as the two other modified branches. These latter

are the tendrils; they are at first thicker and longer than the

middle branch, but never become more than an inch in length. They

taper to a point and are flattened, with the lower clasping surface

destitute of hairs. At first they project straight up; but soon

diverging, spontaneously curl downwards so as to become symmetrically

and elegantly hooked, as represented in the diagram. They are now,

whilst the flower-buds are still small, ready for action.

The two or three upper internodes, whilst young, steadily revolve;

those on one plant made two circles, against the course of the sun,

in 3 hrs. 12 m.; in a second plant the same course was followed, and

the two circles were completed in 3 hrs. 41 m.; in a third plant, the

internodes followed the sun and made two circles in 3 hrs. 47 m. The

average rate of these six revolutions was 1 hr. 46 m. The stem shows

no tendency to twine spirally round a support; but the allied

tendril-bearing genus Paullinia is said (Mohl, p. 4) to be a twiner.

The flower-peduncles, which stand up above the end of the shoot, are

carried round and round by the revolving movement of the internodes;

and when the stem is securely tied, the long and thin flower-

peduncles themselves are seen to be in continued and sometimes rapid

movement from side to side. They sweep a wide space, but only

occasionally revolve in a regular elliptical course. By the combined

movements of the internodes and peduncles, one of the two short

hooked tendrils, sooner or later, catches hold of some twig or

branch, and then it curls round and securely grasps it. These

tendrils are, however, but slightly sensitive; for by rubbing their

under surface only a slight movement is slowly produced. I hooked a

tendril on to a twig; and in 1 hr. 45 m. it was curved considerably

inwards; in 2 hrs. 30 m. it formed a ring; and in from 5 to 6 hours

from being first hooked, it closely grasped the stick. A second

tendril acted at nearly the same rate; but I observed one that took

24 hours before it curled twice round a thin twig. Tendrils which

have caught nothing, spontaneously curl up to a close helix after the

interval of several days. Those which have curled round some object,

soon become a little thicker and tougher. The long and thin main

peduncle, though spontaneously moving, is not sensitive and never

clasps a support. Nor does it ever contract spirally, {33} although

a contraction of this kind apparently would have been of service to

the plant in climbing. Nevertheless it climbs pretty well without

this aid. The seed-capsules though light, are of enormous size

(hence its English name of balloon-vine), and as two or three are

carried on the same peduncle, the tendrils rising close to them may

be of service in preventing their being dashed to pieces by the wind.

In the hothouse the tendrils served simply for climbing.

The position of the tendrils alone suffices to show their homological

nature. In two instances one of two tendrils produced a flower at

its tip; this, however, did not prevent its acting properly and

curling round a twig. In a third case both lateral branches which

ought to have been modified into tendrils, produced flowers like the

central branch, and had quite lost their tendril-structure.

I have seen, but was not enabled carefully to observe, only one other

climbing Sapindaceous plant, namely, Paullinia. It was not in

flower, yet bore long forked tendrils. So that, Paullinia, with

respect to its tendrils, appears to bear the same relation to

Cardiospermum that Cissus does to Vitis.

PASSIFLORACEAE.--After reading the discussion and facts given by Mohl

(p. 47) on the nature of the tendrils in this family, no one can

doubt that they are modified flower-peduncles. The tendrils and the

flower-peduncles rise close side by side; and my son, William E.

Darwin, made sketches for me of their earliest state of development

in the hybrid P. floribunda. The two organs appear at first as a

single papilla which gradually divides; so that the tendril appears

to be a modified branch of the flower-peduncle. My son found one

very young tendril surmounted by traces of floral organs, exactly

like those on the summit of the true flower-peduncle at the same

early age.

Passiflora gracilis.--This well-named, elegant, annual species

differs from the other members of the group observed by me, in the

young internodes having the power of revolving. It exceeds all the

other climbing plants which I have examined, in the rapidity of its

movements, and all tendril-bearers in the sensitiveness of the

tendrils. The internode which carries the upper active tendril and

which likewise carries one or two younger immature internodes, made

three revolutions, following the sun, at an average rate of 1 hr. 4

m.; it then made, the day becoming very hot, three other revolutions

at an average rate of between 57 and 58 m.; so that the average of

all six revolutions was 1 hr. 1 m. The apex of the tendril describes

elongated ellipses, sometimes narrow and sometimes broad, with their

longer axes inclined in slightly different directions. The plant can

ascend a thin upright stick by the aid of its tendrils; but the stem

is too stiff for it to twine spirally round it, even when not

interfered with by the tendrils, these having been successively

pinched off at an early age.

When the stem is secured, the tendrils are seen to revolve in nearly

the same manner and at the same rate as the internodes. {34} The

tendrils are very thin, delicate, and straight, with the exception of

the tips, which are a little curved; they are from 7 to 9 inches in

length. A half-grown tendril is not sensitive; but when nearly full-

grown they are extremely sensitive. A single delicate touch on the

concave surface of the tip soon caused one to curve; and in 2 minutes

it formed an open helix. A loop of soft thread weighing one thirty-

second of a grain (2.02 mg.) placed most gently on the tip, thrice

caused distinct curvature. A bent bit of thin platina wire weighing

only fiftieth of a grain (1.23 mg.) twice produced the same effect;

but this latter weight, when left suspended, did not suffice to cause

a permanent curvature. These trials were made under a bell-glass, so

that the loops of thread and wire were not agitated by the wind. The

movement after a touch is very rapid: I took hold of the lower part

of several tendrils, and then touched their concave tips with a thin

twig and watched them carefully through a lens; the tips evidently

began to bend after the following intervals--31, 25, 32, 31, 28, 39,

31, and 30 seconds; so that the movement was generally perceptible in

half a minute after a touch; but on one occasion it was distinctly

visible in 25 seconds. One of the tendrils which thus became bent in

31 seconds, had been touched two hours previously and had coiled into

a helix; so that in this interval it had straightened itself and had

perfectly recovered its irritability.

To ascertain how often the same tendril would become curved when

touched, I kept a plant in my study, which from being cooler than the

hot-house was not very favourable for the experiment. The extremity

was gently rubbed four or five times with a thin stick, and this was

done as often as it was observed to have become nearly straight again

after having been in action; and in the course of 54 hrs. it answered

to the stimulus 21 times, becoming each time hooked or spiral. On

the last occasion, however, the movement was very slight, and soon

afterwards permanent spiral contraction commenced. No trials were

made during the night, so that the tendril would perhaps have

answered a greater number of times to the stimulus; though, on the

other hand, from having no rest it might have become exhausted from

so many quickly repeated efforts.

I repeated the experiment made on the Echinocystis, and placed

several plants of this Passiflora so close together, that their

tendrils were repeatedly dragged over each other; but no curvature

ensued. I likewise repeatedly flirted small drops of water from a

brush on many tendrils, and syringed others so violently that the

whole tendril was dashed about, but they never became curved. The

impact from the drops of water was felt far more distinctly on my

hand than that from the loops of thread (weighing one thirty-second

of a grain) when allowed to fall on it from a height, and these

loops, which caused the tendrils to become curved, had been placed

most gently on them. Hence it is clear, that the tendrils either

have become habituated to the touch of other tendrils and drops of

rain, or that they were from the first rendered sensitive only to

prolonged though excessively slight pressure of solid objects, with

the exclusion of that from other tendrils. To show the difference in

the kind of sensitiveness in different plants and likewise to show

the force of the syringe used, I may add that the lightest jet from

it instantly caused the leaves of a Mimosa to close; whereas the loop

of thread weighing one thirty-second of a grain, when rolled into a

ball and placed gently on the glands at the bases of the leaflets of

the Mimosa, caused no action.

Passiflora punctata.--The internodes do not move, but the tendrils

revolve regularly. A half-grown and very sensitive tendril made

three revolutions, opposed to the course of the sun, in 3 hrs. 5 m.,

2 hrs. 40 m. and 2 hrs. 50 m.; perhaps it might have travelled more

quickly when nearly full-grown. A plant was placed in front of a

window, and, as with twining stems, the light accelerated the

movement of the tendril in one direction and retarded it in the

other; the semicircle towards the light being performed in one

instance in 15 m. less time and in a second instance in 20 m. less

time than that required by the semicircle towards the dark end of the

room. Considering the extreme tenuity of these tendrils, the action

of the light on them is remarkable. The tendrils are long, and, as

just stated, very thin, with the tip slightly curved or hooked. The

concave side is extremely sensitive to a touch--even a single touch

causing it to curl inwards; it subsequently straightened itself, and

was again ready to act. A loop of soft thread weighing one

fourteenth of a grain (4.625 mg.) caused the extreme tip to bend;

another time I tried to hang the same little loop on an inclined

tendril, but three times it slid off; yet this extraordinarily slight

degree of friction sufficed to make the tip curl. The tendril,

though so sensitive, does not move very quickly after a touch, no

conspicuous movement being observable until 5 or 10 m. had elapsed.

The convex side of the tip is not sensitive to a touch or to a

suspended loop of thread. On one occasion I observed a tendril

revolving with the convex side of the tip forwards, and in

consequence it was not able to clasp a stick, against which it

scraped; whereas tendrils revolving with the concave side forward,

promptly seize any object in their path.

Passiflora quadrangularis.--This is a very distinct species. The

tendrils are thick, long, and stiff; they are sensitive to a touch

only on the concave surface towards the extremity. When a stick was

placed so that the middle of the tendril came into contact with it,

no curvature ensued. In the hothouse a tendril made two revolutions,

each in 2 hrs. 22 m.; in a cool room one was completed in 3 hrs., and

a second in 4 hrs. The internodes do not revolve; nor do those of

the hybrid P. floribunda.

Tacsonia manicata.--Here again the internodes do not revolve. The

tendrils are moderately thin and long; one made a narrow ellipse in 5

hrs. 20 m., and the next day a broad ellipse in 5 hrs. 7 m. The

extremity being lightly rubbed on the concave surface, became just

perceptibly curved in 7 m., distinctly in 10 m., and hooked in 20 m.

We have seen that the tendrils in the last three families, namely,

the Vitaceae, Sapindaceae and Passifloraceae, are modified flower-

peduncles. This is likewise the case, according to De Candolle (as

quoted by Mohl), with the tendrils of Brunnichia, one of the

Polygonaceae. In two or three species of Modecca, one of the

Papayaceae, the tendrils, as I hear from Prof. Oliver, occasionally

bear flowers and fruit; so that they are axial in their nature.

The Spiral Contraction of Tendrils.

This movement, which shortens the tendrils and renders them elastic,

commences in half a day, or in a day or two after their extremities

have caught some object. There is no such movement in any leaf-

climber, with the exception of an occasional trace of it in the

petioles of Tropaeolum tricolorum. On the other hand, the tendrils

of all tendril-bearing plants, contract spirally after they have

caught an object with the following exceptions. Firstly, Corydalis

claviculata, but then this plant might be called a leaf-climber.

Secondly and thirdly, Bignonia unguis with its close allies, and

Cardiospermum; but their tendrils are so short that their contraction

could hardly occur, and would be quite superfluous. Fourthly, Smilax

aspera offers a more marked exception, as its tendrils are moderately

long. The tendrils of Dicentra, whilst the plant is young, are short

and after attachment only become slightly flexuous; in older plants

they are longer and then they contract spirally. I have seen no

other exceptions to the rule that tendrils, after clasping with their

extremities a support, undergo spiral contraction. When, however,

the tendril of a plant of which the stem is immovably fixed, catches

some fixed object, it does not contract, simply because it cannot;

this, however, rarely occurs. In the common Pea the lateral branches

alone contract, and not the central stem; and with most plants, such

as the Vine, Passiflora, Bryony, the basal portion never forms a

spire.

I have said that in Corydalis claviculata the end of the leaf or

tendril (for this part may be indifferently so called) does not

contract into a spire. The branchlets, however, after they have

wound round thin twigs, become deeply sinuous or zigzag. Moreover

the whole end of the petiole or tendril, if it seizes nothing, bends

after a time abruptly downwards and inwards, showing that its outer

surface has gone on growing after the inner surface has ceased to

grow. That growth is the chief cause of the spiral contraction of

tendrils may be safely admitted, as shown by the recent researches of

H. de Vries. I will, however, add one little fact in support of this

conclusion.

If the short, nearly straight portion of an attached tendril of

Passiflora gracilis, (and, as I believe, of other tendrils,) between

the opposed spires, be examined, it will be found to be transversely

wrinkled in a conspicuous manner on the outside; and this would

naturally follow if the outer side had grown more than the inner

side, this part being at the same time forcibly prevented from

becoming curved. So again the whole outer surface of a spirally

wound tendril becomes wrinkled if it be pulled straight.

Nevertheless, as the contraction travels from the extremity of a

tendril, after it has been stimulated by contact with a support, down

to the base, I cannot avoid doubting, from reasons presently to be

given, whether the whole effect ought to be attributed to growth. An

unattached tendril rolls itself up into a flat helix, as in the case

of Cardiospermum, if the contraction commences at the extremity and

is quite regular; but if the continued growth of the outer surface is

a little lateral, or if the process begins near the base, the

terminal portion cannot be rolled up within the basal portion, and

the tendril then forms a more or less open spire. A similar result

follows if the extremity has caught some object, and is thus held

fast.

The tendrils of many kinds of plants, if they catch nothing, contract

after an interval of several days or weeks into a spire; but in these

cases the movement takes place after the tendril has lost its

revolving power and hangs down; it has also then partly or wholly

lost its sensibility; so that this movement can be of no use. The

spiral contraction of unattached tendrils is a much slower process

than that of attached ones. Young tendrils which have caught a

support and are spirally contracted, may constantly be seen on the

same stem with the much older unattached and uncontracted tendrils.

In the Echinocystis I have seen a tendril with the two lateral

branches encircling twigs and contracted into beautiful spires,

whilst the main branch which had caught nothing remained for many

days straight. In this plant I once observed a main branch after it

had caught a stick become spirally flexuous in 7 hrs., and spirally

contracted in 18 hrs. Generally the tendrils of the Echinocystis

begin to contract in from 12 hrs. to 24 hrs. after catching some

object; whilst unattached tendrils do not begin to contract until two

or three or even more days after all revolving movement has ceased.

A full-grown tendril of Passiflora quadrangularis which had caught a

stick began in 8 hrs. to contract, and in 24 hrs. formed several

spires; a younger tendril, only two-thirds grown, showed the first

trace of contraction in two days after clasping a stick, and in two

more days formed several spires. It appears, therefore, that the

contraction does not begin until the tendril is grown to nearly its

full length. Another young tendril of about the same age and length

as the last did not catch any object; it acquired its full length in

four days; in six additional days it first became flexuous, and in

two more days formed one complete spire. This first spire was formed

towards the basal end, and the contraction steadily but slowly

progressed towards the apex; but the whole was not closely wound up

into a spire until 21 days had elapsed from the first observation,

that is, until 17 days after the tendril had grown to its full

length.

The spiral contraction of tendrils is quite independent of their

power of spontaneously revolving, for it occurs in tendrils, such as

those of Lathyrus grandiflorus and Ampelopsis hederacea, which do not

revolve. It is not necessarily related to the curling of the tips

round a support, as we see with the Ampelopsis and Bignonia

capreolata, in which the development of adherent discs suffices to

cause spiral contraction. Yet in some cases this contraction seems

connected with the curling or clasping movement, due to contact with

a support; for not only does it soon follow this act, but the

contraction generally begins close to the curled extremity, and

travels downwards to the base. If, however, a tendril be very slack,

the whole length almost simultaneously becomes at first flexuous and

then spiral. Again, the tendrils of some few plants never contract

spirally unless they have first seized hold of some object; if they

catch nothing they hang down, remaining straight, until they wither

and drop off: this is the case with the tendrils of Bignonia, which

consist of modified leaves, and with those of three genera of the

Vitaceae, which are modified flower-peduncles. But in the great

majority of cases, tendrils which have never come in contact with any

object, after a time contract spirally. All these facts taken

together, show that the act of clasping a support and the spiral

contraction of the whole length of the tendril, are phenomena not

necessarily connected.

The spiral contraction which ensues after a tendril has caught a

support is of high service to the plant; hence its almost universal

occurrence with species belonging to widely different orders. When a

shoot is inclined and its tendril has caught an object above, the

spiral contraction drags up the shoot. When the shoot is upright,

the growth of the stem, after the tendrils have seized some object

above, would leave it slack, were it not for the spiral contraction

which draws up the stem as it increases in length. Thus there is no

waste of growth, and the stretched stem ascends by the shortest

course. When a terminal branchlet of the tendril of Cobaea catches a

stick, we have seen how well the spiral contraction successively

brings the other branchlets, one after the other, into contact with

the stick, until the whole tendril grasps it in an inextricable knot.

When a tendril has caught a yielding object, this is sometimes

enveloped and still further secured by the spiral folds, as I have

seen with Passiflora quadrangularis; but this action is of little

importance.

A far more important service rendered by the spiral contraction of

the tendrils is that they are thus made highly elastic. As before

remarked under Ampelopsis, the strain is thus distributed equally

between the several attached branches; and this renders the whole far

stronger than it otherwise would be, as the branches cannot break

separately. It is this elasticity which protects both branched and

simple tendrils from being torn away from their supports during

stormy weather. I have more than once gone on purpose during a gale

to watch a Bryony growing in an exposed hedge, with its tendrils

attached to the surrounding bushes; and as the thick and thin

branches were tossed to and fro by the wind, the tendrils, had they

not been excessively elastic, would instantly have been torn off and

the plant thrown prostrate. But as it was, the Bryony safely rode

out the gale, like a ship with two anchors down, and with a long

range of cable ahead to serve as a spring as she surges to the storm.

When an unattached tendril contracts spirally, the spire always runs

in the same direction from tip to base. A tendril, on the other

hand, which has caught a support by its extremity, although the same

side is concave from end to end, invariably becomes twisted in one

part in one direction, and in another part in the opposite direction;

the oppositely turned spires being separated by a short straight

portion. This curious and symmetrical structure has been noticed by

several botanists, but has not been sufficiently explained. {35} It

occurs without exception with all tendrils which after catching an

object contract spirally, but is of course most conspicuous in the

longer tendrils. It never occurs with uncaught tendrils; and when

this appears to have occurred, it will be found that the tendril had

originally seized some object and had afterwards been torn free.

Commonly, all the spires at one end of an attached tendril run in one

direction, and all those at the other end in the opposite direction,

with a single short straight portion in the middle; but I have seen a

tendril with the spires alternately turning five times in opposite

directions, with straight pieces between them; and M. Leon has seen

seven or eight such alternations. Whether the spires turn once or

more than once in opposite directions, there are as many turns in the

one direction as in the other. For instance, I gathered ten attached

tendrils of the Bryony, the longest with 33, and the shortest with

only 8 spiral turns; and the number of turns in the one direction was

in every case the same (within one) as in the opposite direction.

The explanation of this curious little fact is not difficult. I will

not attempt any geometrical reasoning, but will give only a practical

illustration. In doing this, I shall first have to allude to a point

which was almost passed over when treating of Twining-plants. If we

hold in our left hand a bundle of parallel strings, we can with our

right hand turn these round and round, thus imitating the revolving

movement of a twining plant, and the strings do not become twisted.

But if we hold at the same time a stick in our left hand, in such a

position that the strings become spirally turned round it, they will

inevitably become twisted. Hence a straight coloured line, painted

along the internodes of a twining plant before it has wound round a

support, becomes twisted or spiral after it has wound round. I

painted a red line on the straight internodes of a Humulus, Mikania,

Ceropegia, Convolvulus, and Phaseolus, and saw it become twisted as

the plant wound round a stick. It is possible that the stems of some

plants by spontaneously turning on their own axes, at the proper rate

and in the proper direction, might avoid becoming twisted; but I have

seen no such case.

In the above illustration, the parallel strings were wound round a

stick; but this is by no means necessary, for if wound into a hollow

coil (as can be done with a narrow slip of elastic paper) there is

the same inevitable twisting of the axis. When, therefore, a free

tendril coils itself into a spire, it must either become twisted

along its whole length (and this never occurs), or the free extremity

must turn round as many times as there are spires formed. It was

hardly necessary to observe this fact; but I did so by affixing

little paper vanes to the extreme points of the tendrils of

Echinocystis and Passiflora quadrangularis; and as the tendril

contracted itself into successive spires, the vane slowly revolved.

We can now understand the meaning of the spires being invariably

turned in opposite directions, in tendrils which from having caught

some object are fixed at both ends. Let us suppose a caught tendril

to make thirty spiral turns all in the same direction; the inevitable

result would be that it would become twisted thirty times on its own

axis. This twisting would not only require considerable force, but,

as I know by trial, would burst the tendril before the thirty turns

were completed. Such cases never really occur; for, as already

stated, when a tendril has caught a support and is spirally

contracted, there are always as many turns in one direction as in the

other; so that the twisting of the axis in the one direction is

exactly compensated by the twisting in the opposite direction. We

can further see how the tendency is given to make the later formed

coils opposite to those, whether turned to the right or to the left,

which are first made. Take a piece of string, and let it hang down

with the lower end fixed to the floor; then wind the upper end

(holding the string quite loosely) spirally round a perpendicular

pencil, and this will twist the lower part of the string; and after

it has been sufficiently twisted, it will be seen to curve itself

into an open spire, with the curves running in an opposite direction

to those round the pencil, and consequently with a straight piece of

string between the opposed spires. In short, we have given to the

string the regular spiral arrangement of a tendril caught at both

ends. The spiral contraction generally begins at the extremity which

has clasped a support; and these first-formed spires give a twist to

the axis of the tendril, which necessarily inclines the basal part

into an opposite spiral curvature. I cannot resist giving one other

illustration, though superfluous: when a haberdasher winds up ribbon

for a customer, he does not wind it into a single coil; for, if he

did, the ribbon would twist itself as many times as there were coils;

but he winds it into a figure of eight on his thumb and little

finger, so that he alternately takes turns in opposite directions,

and thus the ribbon is not twisted. So it is with tendrils, with

this sole difference, that they take several consecutive turns in one

direction and then the same number in an opposite direction; but in

both cases the self-twisting is avoided.

Summary on the Nature and Action of Tendrils.

With the majority of tendril-bearing plants the young internodes

revolve in more or less broad ellipses, like those made by twining

plants; but the figures described, when carefully traced, generally

form irregular ellipsoidal spires. The rate of revolution varies

from one to five hours in different species, and consequently is in

some cases more rapid than with any twining plant, and is never so

slow as with those many twiners which take more than five hours for

each revolution. The direction is variable even in the same

individual plant. In Passiflora, the internodes of only one species

have the power of revolving. The Vine is the weakest revolver

observed by me, apparently exhibiting only a trace of a former power.

In the Eccremocarpus the movement is interrupted by many long pauses.

Very few tendril-bearing plants can spirally twine up an upright

stick. Although the power of twining has generally been lost, either

from the stiffness or shortness of the internodes, from the size of

the leaves, or from some other unknown cause, the revolving movement

of the stem serves to bring the tendrils into contact with

surrounding objects.

The tendrils themselves also spontaneously revolve. The movement

begins whilst the tendril is young, and is at first slow. The mature

tendrils of Bignonia littoralis move much slower than the internodes.

Generally, the internodes and tendrils revolve together at the same

rate; in Cissus, Cobaea, and most Passiflorae, the tendrils alone

revolve; in other cases, as with Lathyrus aphaca, only the internodes

move, carrying with them the motionless tendrils; and, lastly (and

this is the fourth possible case), neither internodes nor tendrils

spontaneously revolve, as with Lathyrus grandiflorus and Ampelopsis.

In most Bignonias, Eccremocarpus Mutisia, and the Fumariaceae, the

internodes, petioles and tendrils all move harmoniously together. In

every case the conditions of life must be favourable in order that

the different parts should act in a perfect manner.

Tendrils revolve by the curvature of their whole length, excepting

the sensitive extremity and the base, which parts do not move, or

move but little. The movement is of the same nature as that of the

revolving internodes, and, from the observations of Sachs and H. de

Vries, no doubt is due to the same cause, namely, the rapid growth of

a longitudinal band, which travels round the tendril and successively

bows each part to the opposite side. Hence, if a line be painted

along that surface which happens at the time to be convex, the line

becomes first lateral, then concave, then lateral, and ultimately

again convex. This experiment can be tried only on the thicker

tendrils, which are not affected by a thin crust of dried paint. The

extremities are often slightly curved or hooked, and the curvature of

this part is never reversed; in this respect they differ from the

extremities of twining shoots, which not only reverse their

curvature, or at least become periodically straight, but curve

themselves in a greater degree than the lower part. In most other

respects a tendril acts as if it were one of several revolving

internodes, which all move together by successively bending to each

point of the compass. There is, however, in many cases this

unimportant difference, that the curving tendril is separated from

the curving internode by a rigid petiole. With most tendril-bearers

the summit of the stem or shoot projects above the point from which

the tendril arises; and it is generally bent to one side, so as to be

out of the way of the revolutions swept by the tendril. In those

plants in which the terminal shoot is not sufficiently out of the

way, as we have seen with the Echinocystis, as soon as the tendril

comes in its revolving course to this point, it stiffens and

straightens itself, and thus rising vertically up passes over the

obstacle in an admirable manner.

All tendrils are sensitive, but in various degrees, to contact with

an object, and curve towards the touched side. With several plants a

single touch, so slight as only just to move the highly flexible

tendril, is enough to induce curvature. Passiflora gracilis

possesses the most sensitive tendrils which I have observed: a bit

of platina wire 0.02 of a grain (1.23 mg.) in weight, gently placed

on the concave point, caused a tendril to become hooked, as did a

loop of soft, thin cotton thread weighing one thirty-second of a

grain (2.02 mg.) With the tendrils of several other plants, loops

weighing one sixteenth of a grain (4.05 mg.) sufficed. The point of

a tendril of Passiflora gracilis began to move distinctly in 25

seconds after a touch, and in many cases after 30 seconds. Asa Gray

also saw movement in the tendrils of the Cucurbitaceous genus,

Sicyos, in 30 seconds. The tendrils of some other plants, when

lightly rubbed, moved in a few minutes; with Dicentra in half-an-

hour; with Smilax in an hour and a quarter or half; and with

Ampelopsis still more slowly. The curling movement consequent on a

single touch continues to increase for a considerable time, then

ceases; after a few hours the tendril uncurls itself, and is again

ready to act. When the tendrils of several kinds of plants were

caused to bend by extremely light weights suspended on them, they

seemed to grow accustomed to so slight a stimulus, and straightened

themselves, as if the loops had been removed. It makes no difference

what sort of object a tendril touches, with the remarkable exception

of other tendrils and drops of water, as was observed with the

extremely sensitive-tendrils of Passiflora gracilis and of the

Echinocystis. I have, however, seen tendrils of the Bryony which had

temporarily caught other tendrils, and often in the case of the vine.

Tendrils of which the extremities are permanently and slightly

curved, are sensitive only on the concave surface; other tendrils,

such as those of the Cobaea (though furnished with horny hooks

directed to one side) and those of Cissus discolor, are sensitive on

all sides. Hence the tendrils of this latter plant, when stimulated

by a touch of equal force on opposite sides, did not bend. The

inferior and lateral surfaces of the tendrils of Mutisia are

sensitive, but not the upper surface. With branched tendrils, the

several branches act alike; but in the Hanburya the lateral spur-like

branch does not acquire (for excellent reasons which have been

explained) its sensitiveness nearly so soon as the main branch. With

most tendrils the lower or basal part is either not at all sensitive,

or sensitive only to prolonged contact. We thus see that the

sensitiveness of tendrils is a special and localized capacity. It is

quite independent of the power of spontaneously revolving; for the

curling of the terminal portion from touch does not in the least

interrupt the former movement. In Bignonia unguis and its close

allies, the petioles of the leaves, as well as the tendrils, are

sensitive to a touch.

Twining plants when they come into contact with a stick, curl round

it invariably in the direction of their revolving movement; but

tendrils curl indifferently to either side, in accordance with the

position of the stick and the side which is first touched. The

clasping movement of the extremity is apparently not steady, but

undulatory or vermicular in its nature, as may be inferred from the

curious manner in which the tendrils of the Echinocystis slowly

crawled round a smooth stick.

As with a few exceptions tendrils spontaneously revolve, it may be

asked,--why have they been endowed with sensitiveness?--why, when

they come into contact with a stick, do they not, like twining

plants, spirally wind round it? One reason may be that they are in

most cases so flexible and thin, that when brought into contact with

any object, they would almost certainly yield and be dragged onwards

by the revolving movement. Moreover, the sensitive extremities have

no revolving power as far as I have observed, and could not by this

means curl round a support. With twining plants, on the other hand,

the extremity spontaneously bends more than any other part; and this

is of high importance for the ascent of the plant, as may be seen on

a windy day. It is, however, possible that the slow movement of the

basal and stiffer parts of certain tendrils, which wind round sticks

placed in their path, may be analogous to that of twining plants.

But I hardly attended sufficiently to this point, and it would have

been difficult to distinguish between a movement due to extremely

dull irritability, from the arrestment of the lower part, whilst the

upper part continued to move onwards.

Tendrils which are only three-fourths grown, and perhaps even at an

earlier age, but not whilst extremely young, have the power of

revolving and of grasping any object which they touch. These two

capacities are generally acquired at about the same period, and both

fail when the tendril is full grown. But in Cobaea and Passiflora

punctata the tendrils begin to revolve in a useless manner, before

they have become sensitive. In the Echinocystis they retain their

sensitiveness for some time after they have ceased to revolve and

after they have sunk downwards; in this position, even if they were

able to seize an object, such power would be of no service in

supporting the stem. It is a rare circumstance thus to detect any

superfluity or imperfection in the action of tendrils--organs which

are so excellently adapted for the functions which they have to

perform; but we see that they are not always perfect, and it would be

rash to assume that any existing tendril has reached the utmost limit

of perfection.

Some tendrils have their revolving motion accelerated or retarded, in

moving to or from the light; others, as with the Pea, seem

indifferent to its action; others move steadily from the light to the

dark, and this aids them in an important manner in finding a support.

For instance, the tendrils of Bignonia capreolata bend from the light

to the dark as truly as a wind-vane from the wind. In the

Eccremocarpus the extremities alone twist and turn about so as to

bring their finer branches and hooks into close contact with any dark

surface, or into crevices and holes.

A short time after a tendril has caught a support, it contracts with

some rare exceptions into a spire; but the manner of contraction and

the several important advantages thus gained have been discussed so

lately, that nothing need here be repeated on the subject. Tendrils

soon after catching a support grow much stronger and thicker, and

sometimes more durable to a wonderful degree; and this shows how much

their internal tissues must be changed. Occasionally it is the part

which is wound round a support which chiefly becomes thicker and

stronger; I have seen, for instance, this part of a tendril of

Bignonia aequinoctialis twice as thick and rigid as the free basal

part. Tendrils which have caught nothing soon shrink and wither; but

in some species of Bignonia they disarticulate and fall off like

leaves in autumn.

Any one who had not closely observed tendrils of many kinds would

probably infer that their action was uniform. This is the case with

the simpler kinds, which simply curl round an object of moderate

thickness, whatever its nature may be. {36} But the genus Bignonia

shows us what diversity of action there may be between the tendrils

of closely allied species. In all the nine species observed by me,

the young internodes revolve vigorously; the tendrils also revolve,

but in some of the species in a very feeble manner; and lastly the

petioles of nearly all revolve, though with unequal power. The

petioles of three of the species, and the tendrils of all are

sensitive to contact. In the first-described species, the tendrils

resemble in shape a bird's foot, and they are of no service to the

stem in spirally ascending a thin upright stick, but they can seize

firm hold of a twig or branch. When the stem twines round a somewhat

thick stick, a slight degree of sensitiveness possessed by the

petioles is brought into play, and the whole leaf together with the

tendril winds round it. In B. unguis the petioles are more

sensitive, and have greater power of movement than those of the last

species; they are able, together with the tendrils, to wind

inextricably round a thin upright stick; but the stem does not twine

so well. B. Tweedyana has similar powers, but in addition, emits

aerial roots which adhere to the wood. In B. venusta the tendrils

are converted into elongated three-pronged grapnels, which move

spontaneously in a conspicuous manner; the petioles, however, have

lost their sensitiveness. The stem of this species can twine round

an upright stick, and is aided in its ascent by the tendrils seizing

the stick alternately some way above and then contracting spirally.

In B. littoralis the tendrils, petioles, and internodes, all revolve

spontaneously. The stem, however, cannot twine, but ascends an

upright stick by seizing it above with both tendrils together, which

then contract into a spire. The tips of these tendrils become

developed into adhesive discs. B. speciosa possesses similar powers

of movement as the last species, but it cannot twine round a stick,

though it can ascend by clasping the stick horizontally with one or

both of its unbranched tendrils. These tendrils continually insert

their pointed ends into minute crevices or holes, but as they are

always withdrawn by the subsequent spiral contraction, the habit

seems to us in our ignorance useless. Lastly, the stem of B.

capreolata twines imperfectly; the much-branched tendrils revolve in

a capricious manner, and bend from the light to the dark; their

hooked extremities, even whilst immature, crawl into crevices, and,

when mature, seize any thin projecting point; in either case they

develop adhesive discs, and these have the power of enveloping the

finest fibres.

In the allied Eccremocarpus the internodes, petioles, and much-

branched tendrils all spontaneously revolve together. The tendrils

do not as a whole turn from the light; but their bluntly-hooked

extremities arrange themselves neatly on any surface with which they

come into contact, apparently so as to avoid the light. They act

best when each branch seizes a few thin stems, like the culms of a

grass, which they afterwards draw together into a solid bundle by the

spiral contraction of all the branches. In Cobaea the finely-

branched tendrils alone revolve; the branches terminate in sharp,

hard, double, little hooks, with both points directed to the same

side; and these turn by well-adapted movements to any object with

which they come into contact. The tips of the branches also crawl

into dark crevices or holes. The tendrils and internodes of

Ampelopsis have little or no power of revolving; the tendrils are but

little sensitive to contact; their hooked extremities cannot seize

thin objects; they will not even clasp a stick, unless in extreme

need of a support; but they turn from the light to the dark, and,

spreading out their branches in contact with any nearly flat surface,

develop discs. These adhere by the secretion of some cement to a

wall, or even to a polished surface; and this is more than the discs

of the Bignonia capreolata can effect.

The rapid development of these adherent discs is one of the most

remarkable peculiarities possessed by any tendrils. We have seen

that such discs are formed by two species of Bignonia, by Ampelopsis,

and, according to Naudin, {37} by the Cucurbitaceous genus Peponopsis

adhaerens. In Anguria the lower surface of the tendril, after it has

wound round a stick, forms a coarsely cellular layer, which closely

fits the wood, but is not adherent; whilst in Hanburya a similar

layer is adherent. The growth of these cellular out-growths depends,

(except in the case of the Haplolophium and of one species of

Ampelopsis,) on the stimulus from contact. It is a singular fact

that three families, so widely distinct as the Bignoniaceae,

Vitaceae, and Cucurbitaceae, should possess species with tendrils

having this remarkable power.

Sachs attributes all the movements of tendrils to rapid growth on the

side opposite to that which becomes concave. These movements consist

of revolving nutation, the bending to and from the light, and in

opposition to gravity, those caused by a touch, and spiral

contraction. It is rash to differ from so great an authority, but I

cannot believe that one at least of these movements--curvature from a

touch--is thus caused. {38} In the first place it may be remarked

that the movement of nutation differs from that due to a touch, in so

far that in some cases the two powers are acquired by the same

tendril at different periods of growth; and the sensitive part of the

tendril does not seem capable of nutation. One of my chief reasons

for doubting whether the curvature from a touch is the result of

growth, is the extraordinary rapidity of the movement. I have seen

the extremity of a tendril of Passiflora gracilis, after being

touched, distinctly bent in 25 seconds, and often in 30 seconds; and

so it is with the thicker tendril of Sicyos. It appears hardly

credible that their outer surfaces could have actually grown in

length, which implies a permanent modification of structure, in so

short a time. The growth, moreover, on this view must be

considerable, for if the touch has been at all rough the extremity is

coiled in two or three minutes into a spire of several turns.

When the extreme tip of the tendril of Echinocystis caught hold of a

smooth stick, it coiled itself in a few hours (as described at p.

132) twice or thrice round the stick, apparently by an undulatory

movement. At first I attributed this movement to the growth of the

outside; black marks were therefore made, and the interspaces

measured, but I could not thus detect any increase in length. Hence

it seems probable in this case and in others, that the curvature of

the tendril from a touch depends on the contraction of the cells

along the concave side. Sachs himself admits {39} that "if the

growth which takes place in the entire tendril at the time of contact

with a support is small, a considerable acceleration occurs on the

convex surface, but in general there is no elongation on the concave

surface, or there may even be a contraction; in the case of a tendril

of Cucurbita this contraction amounted to nearly one-third of the

original length." In a subsequent passage Sachs seems to feel some

difficulty in accounting for this kind of contraction. It must not

however be supposed from the foregoing remarks that I entertain any

doubt, after reading De Vries' observations, about the outer and

stretched surfaces of attached tendrils afterwards increasing in

length by growth. Such increase seems to me quite compatible with

the first movement being independent of growth. Why a delicate touch

should cause one side of a tendril to contract we know as little as

why, on the view held by Sachs, it should lead to extraordinarily

rapid growth of the opposite side. The chief or sole reason for the

belief that the curvature of a tendril when touched is due to rapid

growth, seems to be that tendrils lose their sensitiveness and power

of movement after they have grown to their full length; but this fact

is intelligible, if we bear in mind that all the functions of a

tendril are adapted to drag up the terminal growing shoot towards the

light. Of what use would it be, if an old and full-grown tendril,

arising from the lower part of a shoot, were to retain its power of

clasping a support? This would be of no use; and we have seen with

tendrils so many instances of close adaptation and of the economy of

means, that we may feel assured that they would acquire irritability

and the power of clasping a support at the proper age--namely, youth-

-and would not uselessly retain such power beyond the proper age.

CHAPTER V.--HOOK AND ROOT-CLIMBERS.--CONCLUDING REMARKS.

Plants climbing by the aid of hooks, or merely scrambling over other

plants--Root-climbers, adhesive matter secreted by the rootlets--

General conclusions with respect to climbing plants, and the stages

of their development.

Hook-Climbers.--In my introductory remarks, I stated that, besides

the two first great classes of climbing plants, namely, those which

twine round a support, and those endowed with irritability enabling

them to seize hold of objects by means of their petioles or tendrils,

there are two other classes, hook-climbers and root-climbers. Many

plants, moreover, as Fritz Muller has remarked, {40} climb or

scramble up thickets in a still more simple fashion, without any

special aid, excepting that their leading shoots are generally long

and flexible. It may, however, be suspected from what follows, that

these shoots in some cases tend to avoid the light. The few hook-

climbers which I have observed, namely, Galium aparine, Rubus

australis, and some climbing Roses, exhibit no spontaneous revolving

movement. If they had possessed this power, and had been capable of

twining, they would have been placed in the class of Twiners; for

some twiners are furnished with spines or hooks, which aid them in

their ascent. For instance, the Hop, which is a twiner, has reflexed

hooks as large as those of the Galium; some other twiners have stiff

reflexed hairs; and Dipladenia has a circle of blunt spines at the

bases of its leaves. I have seen only one tendril-bearing plant,

namely, Smilax aspera, which is furnished with reflexed spines; but

this is the case with several branch-climbers in South Brazil and

Ceylon; and their branches graduate into true tendrils. Some few

plants apparently depend solely on their hooks for climbing, and yet

do so efficiently, as certain palms in the New and Old Worlds. Even

some climbing Roses will ascend the walls of a tall house, if covered

with a trellis. How this is effected I know not; for the young

shoots of one such Rose, when placed in a pot in a window, bent

irregularly towards the light during the day and from the light

during the night, like the shoots of any common plant; so that it is

not easy to understand how they could have got under a trellis close

to the wall. {41}

Root-climbers.--A good many plants come under this class, and are

excellent climbers. One of the most remarkable is the Marcgravia

umbellata, the stem of which in the tropical forests of South

America, as I hear from Mr. Spruce, grows in a curiously flattened

manner against the trunks of trees; here and there it puts forth

claspers (roots), which adhere to the trunk, and, if the latter be

slender, completely embrace it. When this plant has climbed to the

light, it produces free branches with rounded stems, clad with sharp-

pointed leaves, wonderfully different in appearance from those borne

by the stem as long as it remains adherent. This surprising

difference in the leaves, I have also observed in a plant of

Marcgravia dubia in my hothouse. Root-climbers, as far as I have

seen, namely, the Ivy (Hedera helix), Ficus repens, and F. barbatus,

have no power of movement, not even from the light to the dark. As

previously stated, the Hoya carnosa (Asclepiadaceae) is a spiral

twiner, and likewise adheres by rootlets even to a flat wall. The

tendril-bearing Bignonia Tweedyana emits roots, which curve half

round and adhere to thin sticks. The Tecoma radicans (Bignoniaceae),

which is closely allied to many spontaneously revolving species,

climbs by rootlets; nevertheless, its young shoots apparently move

about more than can be accounted for by the varying action of the

light.

I have not closely observed many root-climbers, but can give one

curious fact. Ficus repens climbs up a wall just like Ivy; and when

the young rootlets are made to press lightly on slips of glass, they

emit after about a week's interval, as I observed several times,

minute drops of clear fluid, not in the least milky like that exuded

from a wound. This fluid is slightly viscid, but cannot be drawn out

into threads. It has the remarkable property of not soon drying; a

drop, about the size of half a pin's head, was slightly spread out on

glass, and I scattered on it some minute grains of sand. The glass

was left exposed in a drawer during hot and dry weather, and if the

fluid had been water, it would certainly have dried in a few minutes;

but it remained fluid, closely surrounding each grain of sand, during

128 days: how much longer it would have remained I cannot say. Some

other rootlets were left in contact with the glass for about ten days

or a fortnight, and the drops of secreted fluid were now rather

larger, and so viscid that they could be drawn out into threads.

Some other rootlets were left in contact during twenty-three days,

and these were firmly cemented to the glass. Hence we may conclude

that the rootlets first secrete a slightly viscid fluid, subsequently

absorb the watery parts, (for we have seen that the fluid will not

dry by itself,) and ultimately leave a cement. When the rootlets

were torn from the glass, atoms of yellowish matter were left on it,

which were partly dissolved by a drop of bisulphide of carbon; and

this extremely volatile fluid was rendered very much less volatile by

what it had dissolved.

As the bisulphide of carbon has a strong power of softening indurated

caoutchouc, I soaked in it during a short time several rootlets of a

plant which had grown up a plaistered wall; and I then found many

extremely thin threads of transparent, not viscid, excessively

elastic matter, precisely like caoutchouc, attached to two sets of

rootlets on the same branch. These threads proceeded from the bark

of the rootlet at one end, and at the other end were firmly attached

to particles of silex or mortar from the wall. There could be no

mistake in this observation, as I played with the threads for a long

time under the microscope, drawing them out with my dissecting-

needles and letting them spring back again. Yet I looked repeatedly

at other rootlets similarly treated, and could never again discover

these elastic threads. I therefore infer that the branch in question

must have been slightly moved from the wall at some critical period,

whilst the secretion was in the act of drying, through the absorption

of its watery parts. The genus Ficus abounds with caoutchouc, and we

may conclude from the facts just given that this substance, at first

in solution and ultimately modified into an unelastic cement, {42} is

used by the Ficus repens to cement its rootlets to any surface which

it ascends. Whether other plants, which climb by their rootlets,

emit any cement I do not know; but the rootlets of the Ivy, placed

against glass, barely adhered to it, yet secreted a little yellowish

matter. I may add, that the rootlets of the Marcgravia dubia can

adhere firmly to smooth painted wood.

Vanilla aromatica emits aerial roots a foot in length, which point

straight down to the ground. According to Mohl (p. 49), these crawl

into crevices, and when they meet with a thin support, wind round it,

as do tendrils. A plant which I kept was young, and did not form

long roots; but on placing thin sticks in contact with them, they

certainly bent a little to that side, in the course of about a day,

and adhered by their rootlets to the wood; but they did not bend

quite round the sticks, and afterwards they re-pursued their downward

course. It is probable that these slight movements of the roots are

due to the quicker growth of the side exposed to the light, in

comparison with the other side, and not because the roots are

sensitive to contact in the same manner as true tendrils. According

to Mohl, the rootlets of certain species of Lycopodium act as

tendrils. {43}

Concluding Remarks on Climbing Plants.

Plants become climbers, in order, as it may be presumed, to reach the

light, and to expose a large surface of their leaves to its action

and to that of the free air. This is effected by climbers with

wonderfully little expenditure of organized matter, in comparison

with trees, which have to support a load of heavy branches by a

massive trunk. Hence, no doubt, it arises that there are so many

climbing plants in all quarters of the world, belonging to so many

different orders. These plants have been arranged under four

classes, disregarding those which merely scramble over bushes without

any special aid. Hook-climbers are the least efficient of all, at

least in our temperate countries, and can climb only in the midst of

an entangled mass of vegetation. Root-climbers are excellently

adapted to ascend naked faces of rock or trunks of trees; when,

however, they climb trunks they are compelled to keep much in the

shade; they cannot pass from branch to branch and thus cover the

whole summit of a tree, for their rootlets require long-continued and

close contact with a steady surface in order to adhere. The two

great classes of twiners and of plants with sensitive organs, namely,

leaf-climbers and tendril-bearers taken together, far exceed in

number and in the perfection of their mechanism the climbers of the

two first classes. Those which have the power of spontaneously

revolving and of grasping objects with which they come in contact,

easily pass from branch to branch, and securely ramble over a wide,

sun-lit surface.

The divisions containing twining plants, leaf-climbers, and tendril-

bearers graduate to a certain extent into one another, and nearly all

have the same remarkable power of spontaneously revolving. Does this

gradation, it may be asked, indicate that plants belonging to one

subdivision have actually passed during the lapse of ages, or can

pass, from one state to the other? Has, for instance, any tendril-

bearing plant assumed its present structure without having previously

existed as a leaf-climber or a twiner? If we consider leaf-climbers

alone, the idea that they were primordially twiners is forcibly

suggested. The internodes of all, without exception, revolve in

exactly the same manner as twiners; some few can still twine well,

and many others in an imperfect manner. Several leaf-climbing genera

are closely allied to other genera which are simple twiners. It

should also be observed, that the possession of leaves with sensitive

petioles, and with the consequent power of clasping an object, would

be of comparatively little use to a plant, unless associated with

revolving internodes, by which the leaves are brought into contact

with a support; although no doubt a scrambling plant would be apt, as

Professor Jaeger has remarked, to rest on other plants by its leaves.

On the other hand, revolving internodes, without any other aid,

suffice to give the power of climbing; so that it seems probable that

leaf-climbers were in most cases at first twiners, and subsequently

became capable of grasping a support; and this, as we shall presently

see, is a great additional advantage.

From analogous reasons, it is probable that all tendril-bearers were

primordially twiners, that is, are the descendants of plants having

this power and habit. For the internodes of the majority revolve;

and, in a few species, the flexible stem still retains the capacity

of spirally twining round an upright stick. Tendril-bearers have

undergone much more modification than leaf-climbers; hence it is not

surprising that their supposed primordial habits of revolving and

twining have been more frequently lost or modified than in the case

of leaf-climbers. The three great tendril-bearing families in which

this loss has occurred in the most marked manner, are the

Cucurbitaceae, Passifloraceae, and Vitaceae. In the first, the

internodes revolve; but I have heard of no twining form, with the

exception (according to Palm, p. 29. 52) of Momordica balsamina, and

this is only an imperfect twiner. In the two other families I can

hear of no twiners; and the internodes rarely have the power of

revolving, this power being confined to the tendrils. The

internodes, however, of Passiflora gracilis have the power in a

perfect manner, and those of the common Vine in an imperfect degree:

so that at least a trace of the supposed primordial habit has been

retained by some members of all the larger tendril-bearing groups.

On the view here given, it may be asked, Why have the species which

were aboriginally twiners been converted in so many groups into leaf-

climbers or tendril-bearers? Of what advantage has this been to

them? Why did they not remain simple twiners? We can see several

reasons. It might be an advantage to a plant to acquire a thicker

stem, with short internodes bearing many or large leaves; and such

stems are ill fitted for twining. Any one who will look during windy

weather at twining plants will see that they are easily blown from

their support; not so with tendril-bearers or leaf-climbers, for they

quickly and firmly grasp their support by a much more efficient kind

of movement. In those plants which still twine, but at the same time

possess tendrils or sensitive petioles, as some species of Bignonia,

Clematis, and Tropaeolum, it can readily be observed how incomparably

better they grasp an upright stick than do simple twiners. Tendrils,

from possessing this power of grasping an object, can be made long

and thin; so that little organic matter is expended in their

development, and yet they sweep a wide circle in search of a support.

Tendril-bearers can, from their first growth, ascend along the outer

branches of any neighbouring bush, and they are thus always fully

exposed to the light; twiners, on the contrary, are best fitted to

ascend bare stems, and generally have to start in the shade. Within

tall and dense tropical forests, twining plants would probably

succeed better than most kinds of tendril-bearers; but the majority

of twiners, at least in our temperate regions, from the nature of

their revolving movement, cannot ascend thick trunks, whereas this

can be affected by tendril-bearers if the trunks are branched or bear

twigs, and by some species if the bark is rugged.

The advantage gained by climbing is to reach the light and free air

with as little expenditure of organic matter as possible; now, with

twining plants, the stem is much longer than is absolutely necessary;

for instance, I measured the stem of a kidney-bean, which had

ascended exactly two feet in height, and it was three feet in length:

the stem of a pea, on the other hand, which had ascended to the same

height by the aid of its tendrils, was but little longer than the

height reached. That this saving of the stem is really an advantage

to climbing plants, I infer from the species that still twine but are

aided by clasping petioles or tendrils, generally making more open

spires than those made by simple twiners. Moreover, the plants thus

aided, after taking one or two turns in one direction, generally

ascend for a space straight, and then reverse the direction of their

spire. By this means they ascend to a considerably greater height,

with the same length of stem, than would otherwise have been

possible; and they do this with safety, as they secure themselves at

intervals by their clasping petioles or tendrils.

We have seen that tendrils consist of various organs in a modified

state, namely, leaves, flower-peduncles, branches, and perhaps

stipules. With respect to leaves, the evidence of their modification

is ample. In young plants of Bignonia the lower leaves often remain

quite unchanged, whilst the upper ones have their terminal leaflets

converted into perfect tendrils; in Eccremocarpus I have seen a

single lateral branch of a tendril replaced by a perfect leaflet; in

Vicia sativa, on the other hand, leaflets are sometimes replaced by

tendril-branches; and many other such cases could be given. But he

who believes in the slow modification of species will not be content

simply to ascertain the homological nature of different kinds of

tendrils; he will wish to learn, as far as is possible, by what

actual steps leaves, flower-peduncles, &c., have had their functions

wholly changed, and have come to serve merely as prehensile organs.

In the whole group of leaf-climbers abundant evidence has been given

that an organ, still subserving the functions of a leaf, may become

sensitive to a touch, and thus grasp an adjoining object. With

several leaf-climbers the true leaves spontaneously revolve; and

their petioles, after clasping a support grow thicker and stronger.

We thus see that leaves may acquire all the leading and

characteristic qualities of tendrils, namely, sensitiveness,

spontaneous movement, and subsequently increased strength. If their

blades or laminae were to abort, they would form true tendrils. And

of this process of abortion we can follow every step, until no trace

of the original nature of the tendril is left. In Mutisia clematis,

the tendril, in shape and colour, closely resembles the petiole of

one of the ordinary leaves, together with the midribs of the

leaflets, but vestiges of the laminae are still occasionally

retained. In four genera of the Fumariaceae we can follow the whole

process of transformation. The terminal leaflets of the leaf-

climbing Fumaria officinalis are not smaller than the other leaflets;

those of the leaf-climbing Adlumia cirrhosa are greatly reduced;

those of Corydalis claviculata (a plant which may indifferently be

called a leaf-climber or a tendril-bearer) are either reduced to

microscopical dimensions or have their blades wholly aborted, so that

this plant is actually in a state of transition; and, finally, in the

Dicentra the tendrils are perfectly characterized. If, therefore, we

could behold at the same time all the progenitors of Dicentra, we

should almost certainly see a series like that now exhibited by the

above-named three genera. In Tropaeolum tricolorum we have another

kind of passage; for the leaves which are first formed on the young

stems are entirely destitute of laminae, and must be called tendrils,

whilst the later formed leaves have well-developed laminae. In all

cases the acquirement of sensitiveness by the mid-ribs of the leaves

appears to stand in some close relation with the abortion of their

laminae or blades.

On the view here given, leaf-climbers were primordially twiners, and

tendril-bearers (when formed of modified leaves) were primordially

leaf-climbers. The latter, therefore, are intermediate in nature

between twiners and tendril-bearers, and ought to be related to both.

This is the case: thus the several leaf-climbing species of the

Antirrhineae, of Solanum, Cocculus, and Gloriosa, have within the

same family and even within the same genus, relatives which are

twiners. In the genus Mikania, there are leaf-climbing and twining

species. The leaf-climbing species of Clematis are very closely

allied to the tendril-bearing Naravelia. The Fumariaceae include

closely allied genera which are leaf-climbers and tendril-bearers.

Lastly, a species of Bignonia is at the same time both a leaf-climber

and a tendril-bearer; and other closely allied species are twiners.

Tendrils of another kind consist of modified flower-peduncles. In

this case we likewise have many interesting transitional states. The

common Vine (not to mention the Cardiospermum) gives us every

possible gradation between a perfectly developed tendril and a

flower-peduncle covered with flowers, yet furnished with a branch,

forming the flower-tendril. When the latter itself bears a few

flowers, as we know sometimes is the case, and still retains the

power of clasping a support, we see an early condition of all those

tendrils which have been formed by the modification of flower-

peduncles.

According to Mohl and others, some tendrils consist of modified

branches: I have not observed any such cases, and know nothing of

their transitional states, but these have been fully described by

Fritz Muller. The genus Lophospermum also shows us how such a

transition is possible; for its branches spontaneously revolve and

are sensitive to contact. Hence, if the leaves on some of the

branches of the Lophospermum were to abort, these branches would be

converted into true tendrils. Nor is there anything improbable in

certain branches alone being thus modified, whilst others remained

unaltered; for we have seen with certain varieties of Phaseolus, that

some of the branches are thin, flexible, and twine, whilst other

branches on the same plant are stiff and have no such power.

If we inquire how a petiole, a branch or flower-peduncle first became

sensitive to a touch, and acquired the power of bending towards the

touched side, we get no certain answer. Nevertheless an observation

by Hofmeister {44} well deserves attention, namely, that the shoots

and leaves of all plants, whilst young, move after being shaken.

Kerner also finds, as we have seen, that the flower-peduncles of a

large number of plants, if shaken or gently rubbed bend to this side.

And it is young petioles and tendrils, whatever their homological

nature may be, which move on being touched. It thus appears that

climbing plants have utilized and perfected a widely distributed and

incipient capacity, which capacity, as far as we can see, is of no

service to ordinary plants. If we further inquire how the stems,

petioles, tendrils, and flower-peduncles of climbing plants first

acquired their power of spontaneously revolving, or, to speak more

accurately, of successively bending to all points of the compass, we

are again silenced, or at most can only remark that the power of

moving, both spontaneously and from various stimulants, is far more

common with plants, than is generally supposed to be the case by

those who have not attended to the subject. I have given one

remarkable instance, namely that of the Maurandia semperflorens, the

young flower-peduncles of which spontaneously revolve in very small

circles, and bend when gently rubbed to the touched side; yet this

plant certainly does not profit by these two feebly developed powers.

A rigorous examination of other young plants would probably show

slight spontaneous movements in their stems, petioles or peduncles,

as well as sensitiveness to a touch. {45} We see at least that the

Maurandia might, by a little augmentation of the powers which it

already possesses, come first to grasp a support by its flower-

peduncles, and then, by the abortion of some of its flowers (as with

Vitis or Cardiospermum), acquire perfect tendrils.

There is one other interesting point which deserves notice. We have

seen that some tendrils owe their origin to modified leaves, and

others to modified flower-peduncles; so that some are foliar and

others axial in their nature. It might therefore have been expected

that they would have presented some difference in function. This is

not the case. On the contrary, they present the most complete

identity in their several characteristic powers. Tendrils of both

kinds spontaneously revolve at about the same rate. Both, when

touched, bend quickly to the touched side, and afterwards recover

themselves and are able to act again. In both the sensitiveness is

either confined to one side or extends all round the tendril. Both

are either attracted or repelled by the light. The latter property

is seen in the foliar tendrils of Bignonia capreolata and in the

axial tendrils of Ampelopsis. The tips of the tendrils in these two

plants become, after contact, enlarged into discs, which are at first

adhesive by the secretion of some cement. Tendrils of both kinds,

soon after grasping a support, contract spirally; they then increase

greatly in thickness and strength. When we add to these several

points of identity the fact that the petiole of Solanum jasminoides,

after it has clasped a support, assumes one of the most

characteristic features of the axis, namely, a closed ring of woody

vessels, we can hardly avoid asking, whether the difference between

foliar and axial organs can be of so fundamental a nature as is

generally supposed? {46}

We have attempted to trace some of the stages in the genesis of

climbing plants. But, during the endless fluctuations of the

conditions of life to which all organic beings have been exposed, it

might be expected that some climbing plants would have lost the habit

of climbing. In the cases given of certain South African plants

belonging to great twining families, which in their native country

never twine, but reassume this habit when cultivated in England, we

have a case in point. In the leaf-climbing Clematis flammula, and in

the tendril-bearing Vine, we see no loss in the power of climbing,

but only a remnant of the revolving power which is indispensable to

all twiners, and is so common as well as so advantageous to most

climbers. In Tecoma radicans, one of the Bignoniaceae, we see a last

and doubtful trace of the power of revolving.

With respect to the abortion of tendrils, certain cultivated

varieties of Cucurbita pepo have, according to Naudin, {47} either

quite lost these organs or bear semi-monstrous representatives of

them. In my limited experience, I have met with only one apparent

instance of their natural suppression, namely, in the common bean.

All the other species of Vicia, I believe, bear tendrils; but the

bean is stiff enough to support its own stem, and in this species, at

the end of the petiole, where, according to analogy, a tendril ought

to have existed, a small pointed filament projects, about a third of

an inch in length, and which is probably the rudiment of a tendril.

This may be the more safely inferred, as in young and unhealthy

specimens of other tendril-bearing plants similar rudiments may

occasionally be observed. In the bean these filaments are variable

in shape, as is so frequently the case with rudimentary organs; they

are either cylindrical, or foliaceous, or are deeply furrowed on the

upper surface. They have not retained any vestige of the power of

revolving. It is a curious fact, that many of these filaments, when

foliaceous, have on their lower surfaces, dark-coloured glands like

those on the stipules, which excrete a sweet fluid; so that these

rudiments have been feebly utilized.

One other analogous case, though hypothetical, is worth giving.

Nearly all the species of Lathyrus possesses tendrils; but L.

nissolia is destitute of them. This plant has leaves, which must

have struck everyone with surprise who has noticed them, for they are

quite unlike those of all common papilionaceous plants, and resemble

those of a grass. In another species, L. aphaca, the tendril, which

is not highly developed (for it is unbranched, and has no spontaneous

revolving-power), replaces the leaves, the latter being replaced in

function by large stipules. Now if we suppose the tendrils of L.

aphaca to become flattened and foliaceous, like the little

rudimentary tendrils of the bean, and the large stipules to become at

the same time reduced in size, from not being any longer wanted, we

should have the exact counterpart of L. nissolia, and its curious

leaves are at once rendered intelligible to us.

It may be added, as serving to sum up the foregoing views on the

origin of tendril-bearing plants, that L. nissolia is probably

descended from a plant which was primordially a twiner; this then

became a leaf-climber, the leaves being afterwards converted by

degrees into tendrils, with the stipules greatly increased in size

through the law of compensation. {48} After a time the tendrils lost

their branches and became simple; they then lost their revolving-

power (in which state they would have resembled the tendrils of the

existing L. aphaca), and afterwards losing their prehensile power and

becoming foliaceous would no longer be thus designated. In this last

stage (that of the existing L. nissolia) the former tendrils would

reassume their original function of leaves, and the stipules which

were recently much developed being no longer wanted, would decrease

in size. If species become modified in the course of ages, as almost

all naturalists now admit, we may conclude that L. nissolia has

passed through a series of changes, in some degree like those here

indicated.

The most interesting point in the natural history of climbing plants

is the various kinds of movement which they display in manifest

relation to their wants. The most different organs--stems, branches,

flower-peduncles, petioles, mid-ribs of the leaf and leaflets, and

apparently aerial roots--all possess this power.

The first action of a tendril is to place itself in a proper

position. For instance, the tendril of Cobaea first rises vertically

up, with its branches divergent and with the terminal hooks turned

outwards; the young shoot at the extremity of the stem is at the same

time bent to one side, so as to be out of the way. The young leaves

of Clematis, on the other hand, prepare for action by temporarily

curving themselves downwards, so as to serve as grapnels.

Secondly, if a twining plant or a tendril gets by any accident into

an inclined position, it soon bends upwards, though secluded from the

light. The guiding stimulus no doubt is the attraction of gravity,

as Andrew Knight showed to be the case with germinating plants. If a

shoot of any ordinary plant be placed in an inclined position in a

glass of water in the dark, the extremity will, in a few hours, bend

upwards; and if the position of the shoot be then reversed, the

downward-bent shoot reverses its curvature; but if the stolen of a

strawberry, which has no tendency to grow upwards, be thus treated,

it will curve downwards in the direction of, instead of in opposition

to, the force of gravity. As with the strawberry, so it is generally

with the twining shoots of the Hibbertia dentata, which climbs

laterally from bush to bush; for these shoots, if placed in a

position inclined downwards, show little and sometimes no tendency to

curve upwards.

Thirdly, climbing plants, like other plants, bend towards the light

by a movement closely analogous to the incurvation which causes them

to revolve, so that their revolving movement is often accelerated or

retarded in travelling to or from the light. On the other hand, in a

few instances tendrils bend towards the dark.

Fourthly, we have the spontaneous revolving movement which is

independent of any outward stimulus, but is contingent on the youth

of the part, and on vigorous health; and this again of course depends

on a proper temperature and other favourable conditions of life.

Fifthly, tendrils, whatever their homological nature may be, and the

petioles or tips of the leaves of leaf-climbers, and apparently

certain roots, all have the power of movement when touched, and bend

quickly towards the touched side. Extremely slight pressure often

suffices. If the pressure be not permanent, the part in question

straightens itself and is again ready to bend on being touched.

Sixthly, and lastly, tendrils, soon after clasping a support, but not

after a mere temporary curvature, contract spirally. If they have

not come into contact with any object, they ultimately contract

spirally, after ceasing to revolve; but in this case the movement is

useless, and occurs only after a considerable lapse of time.

With respect to the means by which these various movements are

effected, there can be little doubt from the researches of Sachs and

H. de Vries, that they are due to unequal growth; but from the

reasons already assigned, I cannot believe that this explanation

applies to the rapid movements from a delicate touch.

Finally, climbing plants are sufficiently numerous to form a

conspicuous feature in the vegetable kingdom, more especially in

tropical forests. America, which so abounds with arboreal animals,

as Mr. Bates remarks, likewise abounds according to Mohl and Palm

with climbing plants; and of the tendril-bearing plants examined by

me, the highest developed kinds are natives of this grand continent,

namely, the several species of Bignonia, Eccremocarpus, Cobaea, and

Ampelopsis. But even in the thickets of our temperate regions the

number of climbing species and individuals is considerable, as will

be found by counting them. They belong to many and widely different

orders. To gain some rude idea of their distribution in the

vegetable series, I marked, from the lists given by Mohl and Palm

(adding a few myself, and a competent botanist, no doubt, could have

added many more), all those families in Lindley's 'Vegetable Kingdom'

which include twiners, leaf-climbers, or tendril-bearers. Lindley

divides Phanerogamic plants into fifty-nine Alliances; of these, no

less than thirty-five include climbing plants of the above kinds,

hook and root-climbers being excluded. To these a few Cryptogamic

plants must be added. When we reflect on the wide separation of

these plants in the series, and when we know that in some of the

largest, well-defined orders, such as the Compositae, Rubiaceae,

Scrophulariaceae, Liliaceae, &c., species in only two or three genera

have the power of climbing, the conclusion is forced on our minds

that the capacity of revolving, on which most climbers depend, is

inherent, though undeveloped, in almost every plant in the vegetable

kingdom.

It has often been vaguely asserted that plants are distinguished from

animals by not having the power of movement. It should rather be

said that plants acquire and display this power only when it is of

some advantage to them; this being of comparatively rare occurrence,

as they are affixed to the ground, and food is brought to them by the

air and rain. We see how high in the scale of organization a plant

may rise, when we look at one of the more perfect tendril-bearers.

It first places its tendrils ready for action, as a polypus places

its tentacula. If the tendril be displaced, it is acted on by the

force of gravity and rights it self. It is acted on by the light,

and bends towards or from it, or disregards it, whichever may be most

advantageous. During several days the tendrils or internodes, or

both, spontaneously revolve with a steady motion. The tendril

strikes some object, and quickly curls round and firmly grasps it.

In the course of some hours it contracts into a spire, dragging up

the stem, and forming an excellent spring. All movements now cease.

By growth the tissues soon become wonderfully strong and durable.

The tendril has done its work, and has done it in an admirable

manner.

Footnotes:

{1} An English translation of the 'Lehrbuch der Botanik' by

Professor Sachs, has recently (1875), appeared under the title of

'Text-Book of Botany,' and this is a great boon to all lovers of

natural science in England.

{2} 'Proc. Amer. Acad. of Arts and Sciences,' vol. iv. Aug. 12,

1858, p. 98.

{3} Ludwig H. Palm, 'Ueber das Winden der Pflanzen;' Hugo von Mohl,

'Ueber den Bau und des Winden der Ranken und Schlingpflanzen,' 1827.

Palm's Treatise was published only a few weeks before Mohl's. See

also 'The Vegetable Cell' (translated by Henfrey), by H. von Mohl, p.

147 to end.

{4} "Des Mouvements revolutife Respontanes," &c., 'Comptes Rendus,'

tom. xvii. (1843) p. 989; "Recherches sur la Volubilite des Tiges,"

&c., tom. xix. (1844) p. 295.

{5} 'Bull. Bot Soc. de France,' tom. v. 1858, p. 356.

{6} This whole subject has been ably discussed and explained by H.

de Vries, 'Arbeiten des Bot. Instituts in Wurzburg,' Heft iii. pp.

331, 336. See also Sachs ('Text-Book of Botany,' English

translation, 1875, p. 770), who concludes "that torsion is the result

of growth continuing in the outer layers after it has ceased or begun

to cease in the inner layers."

{7} Professor Asa Gray has remarked to me, in a letter, that in

Thuja occidentalis the twisting of the bark is very conspicuous. The

twist is generally to the right of the observer; but, in noticing

about a hundred trunks, four or five were observed to be twisted in

an opposite direction. The Spanish chestnut is often much twisted:

there is an interesting article on this subject in the 'Scottish

Farmer,' 1865, p. 833.

{8} It is well known that the stems of many plants occasionally

become spirally twisted in a monstrous manner; and after my paper was

read before the Linnean Society, Dr. Maxwell Masters remarked to me

in a letter that "some of these cases, if not all, are dependent upon

some obstacle or resistance to their upward growth." This conclusion

agrees with what I have said about the twisting of stems, which have

twined round rugged supports; but does not preclude the twisting

being of service to the plant by giving greater rigidity to the stem.

{9} The view that the revolving movement or nutation of the stems of

twining plants is due to growth is that advanced by Sachs and H. de

Vries; and the truth of this view is proved by their excellent

observations.

{10} The mechanism by which the end of the shoot remains hooked

appears to be a difficult and complex problem, discussed by Dr. H. de

Vries (ibid. p. 337): he concludes that "it depends on the relation

between the rapidity of torsion and the rapidity of nutation."

{11} Dr. H. de Vries also has shown (ibid. p. 321 and 325) by a

better method than that employed by me, that the stems of twining

plants are not irritable, and that the cause of their winding up a

support is exactly what I have described.

{12} Dr. H. de Vries states (ibid. p. 322) that the stem of Cuscuta

is irritable like a tendril.

{13} See Dr. H. de Vries (ibid. p. 324) on this subject.

{14} Comptes Rendus, 1844, tom. xix. p. 295, and Annales des Sc. Nat

3rd series, Bot., tom. ii. p. 163.

{15} I am much indebted to Dr. Hooker for having sent me many plants

from Kew; and to Mr. Veitch, of the Royal Exotic Nursery, for having

generously given me a collection of fine specimens of climbing

plants. Professor Asa Gray, Prof. Oliver, and Dr. Hooker have

afforded me, as on many previous occasions, much information and many

references.

{16} Journal of the Linn. Soc. (Bot.) vol. ix. p. 344. I shall have

occasion often to quote this interesting paper, in which he corrects

or confirms various statements made by me.

{17} I raised nine plants of the hybrid Loasa Herbertii, and six of

these also reversed their spire in ascending a support.

{18} In another genus, namely Davilla, belonging to the same family

with Hibbertia, Fritz Muller says (ibid. p. 349) that "the stem

twines indifferently from left to right, or from right to left; and I

once saw a shoot which ascended a tree about five inches in diameter,

reverse its course in the same manner as so frequently occurs with

Loasa."

{19} Fritz Muller states (ibid. p. 349) that he saw on one occasion

in the forests of South Brazil a trunk about five feet in

circumference spirally ascended by a plant, apparently belonging to

the Menispermaceae. He adds in his letter to me that most of the

climbing plants which there ascend thick trees, are root-climbers;

some being tendril-bearers.

{20} Fritz Muller has published some interesting facts and views on

the structure of the wood of climbing plants in 'Bot. Zeitung,' 1866,

pp. 57, 66.

{21} It appears from A. Kerner's interesting observations, that the

flower-peduncles of a large number of plants are irritable, and bend

when they are rubbed or shaken: Die Schutzmittel des Pollens, 1873,

p. 34.

{22} I have already referred to the case of the twining stem of

Cuscuta, which, according to H. de Vries (ibid. p. 322) is sensitive

to a touch like a tendril.

{23} Dr. Maxwell Masters informs me that in almost all petioles

which are cylindrical, such as those bearing peltate leaves, the

woody vessels form a closed ring; semilunar bands of vessels being

confined to petioles which are channelled along their upper surfaces.

In accordance with this statement, it may be observed that the

enlarged and clasped petiole of the Solanum, with its closed ring of

woody vessels, has become more cylindrical than it was in its

original unclasped condition.

{24} Never having had the opportunity of examining tendrils produced

by the modification of branches, I spoke doubtfully about them in

this essay when originally published. But since then Fritz Muller

has described (Journal of Linn. Soc. vol. ix. p. 344) many striking

cases in South Brazil. In speaking of plants which climb by the aid

of their branches, more or less modified, he states that the

following stages of development can be traced: (1.) Plants

supporting themselves simply by their branches stretched out at right

angles--for example, Chiococca. (2.) Plants clasping a support with

their unmodified branches, as with Securidaca. (3.) Plants climbing

by the extremities of their branches which appear like tendrils, as

is the case according to Endlicher with Helinus. (4.) Plants with

their branches much modified and temporarily converted into tendrils,

but which may be again transformed into branches, as with certain

Papilionaceous plants. (5.) Plants with their branches forming true

tendrils, and used exclusively for climbing--as with Strychnos and

Caulotretus. Even the unmodified branches become much thickened when

they wind round a support. I may add that Mr. Thwaites sent me from

Ceylon a specimen of an Acacia which had climbed up the trunk of a

rather large tree, by the aid of tendril-like, curved or convoluted

branchlets, arrested in their growth and furnished with sharp

recurved hooks.

{25} As far as I can make out, the history of our knowledge of

tendrils is as follows:- We have seen that Palm and von Mohl observed

about the same time the singular phenomenon of the spontaneous

revolving movement of twining-plants. Palm (p. 58), I presume,

observed likewise the revolving movement of tendrils; but I do not

feel sure of this, for he says very little on the subject. Dutrochet

fully described this movement of the tendril in the common pea. Mohl

first discovered that tendrils are sensitive to contact; but from

some cause, probably from observing too old tendrils, he was not

aware how sensitive they were, and thought that prolonged pressure

was necessary to excite their movement. Professor Asa Gray, in a

paper already quoted, first noticed the extreme sensitiveness and

rapidity of the movements of the tendrils of certain Cucurbitaceous

plants.

{26} Fritz Muller states (ibid. p. 348) that in South Brazil the

trifid tendrils of Haplolophium, (one of the Bignoniaceae) without

having come into contact with any object, terminate in smooth shining

discs. These, however, after adhering to any object, sometimes

become considerably enlarged.

{27} Comptes Rendus, tom. xvii. 1843, p. 989.

{28} 'Lecons de Botanique,' &c., 1841, p. 170.

{29} I am indebted to Prof. Oliver for information on this head. In

the Bulletin de la Societe Botanique de France, 1857, there are

numerous discussions on the nature of the tendrils in this family.

{30} 'Gardeners' Chronicle,' 1864, p. 721. From the affinity of the

Cucurbitaceae to the Passifloraceae, it might be argued that the

tendrils of the former are modified flower-peduncles, as is certainly

the case with those of Passion flowers. Mr. R. Holland (Hardwicke's

'Science-Gossip,' 1865, p. 105) states that "a cucumber grew, a few

years ago in my own garden, where one of the short prickles upon the

fruit had grown out into a long, curled tendril."

{31} Trans. Phil. Soc. 1812, p. 314.

{32} Dr. M'Nab remarks (Trans. Bot. Soc. Edinburgh, vol xi. p. 292)

that the tendrils of Amp. Veitchii bear small globular discs before

they have came into contact with any object; and I have since

observed the same fact. These discs, however, increase greatly in

size, if they press against and adhere to any surface. The tendrils,

therefore, of one species of Ampelopsis require the stimulus of

contact for the first development of their discs, whilst those of

another species do not need any such stimulus. We have seen an

exactly parallel case with two species of Bignoniaceae.

{33} Fritz Muller remarks (ibid. p. 348) that a related genus,

Serjania, differs from Cardiospermum in bearing only a single

tendril; and that the common peduncle contracts spirally, when, as

frequently happens, the tendril has clasped the plant's own stem.

{34} Prof. Asa Gray informs me that the tendrils of P. sicyoides

revolve even at a quicker rate than those of P. gracilis; four

revolutions were completed (the temperature varying from 88 degrees-

92 degrees Fahr.) in the following times, 40 m., 45 m., 38.5 m., and

46 m. One half-revolution was performed in 15 m.

{35} See M. Isid. Leon in Bull. Soc. Bot. de France, tom. v. 1858,

p. 650. Dr. H. de Vries points out (p. 306) that I have overlooked,

in the first edition of this essay, the following sentence by Mohl:

"After a tendril has caught a support, it begins in some days to wind

into a spire, which, since the tendril is made fast at both

extremities, must of necessity be in some places to the right, in

others to the left." But I am not surprised that this brief

sentence, without any further explanation did not attract my

attention.

{36} Sachs, however ('Text-Book of Botany,' Eng. Translation, 1875,

p. 280), has shown that which I overlooked, namely, that the tendrils

of different species are adapted to clasp supports of different

thicknesses. He further shows that after a tendril has clasped a

support it subsequently tightens its hold.

{37} Annales des Sc. Nat. Bot. 4th series, tom. xii. p. 89.

{38} It occurred to me that the movement of notation and that from a

touch might be differently affected by anaesthetics, in the same

manner as Paul Bert has shown to be the case with the sleep-movements

of Mimosa and those from a touch. I tried the common pea and

Passiflora gracilis, but I succeeded only in observing that both

movements were unaffected by exposure for 1.5 hrs. to a rather large

dose of sulphuric ether. In this respect they present a wonderful

contrast with Drosera, owing no doubt to the presence of absorbent

glands in the latter plant.

{39} Text-Book of Botany, 1875, p. 779.

{40} Journal of Linn. Soc. vol. ix. p. 348. Professor G. Jaeger has

well remarked ('In Sachen Darwin's, insbesondere contra Wigand,'

1874, p. 106) that it is highly characteristic of climbing plants to

produce thin, elongated, and flexible stems. He further remarks that

plants growing beneath other and taller species or trees, are

naturally those which would be developed into climbers; anti such

plants, from stretching towards the light, and from not being much

agitated by the wind, tend to produce long, thin and flexible shoots.

{41} Professor Asa Gray has explained, as it would appear, this

difficulty in his review (American Journal of Science, vol. xl. Sept.

1865, p. 282) of the present work. He has observed that the strong

summer shoots of the Michigan rose (Rosa setigera) are strongly

disposed to push into dark crevices and away from the light, so that

they would be almost sure to place themselves under a trellis. He

adds that the lateral shoots, made on the following spring emerged

from the trellis as they sought the light.

{42} Mr. Spiller has recently shown (Chemical Society, Feb. 16,

1865), in a paper on the oxidation of india-rubber or caoutchouc,

that this substance, when exposed in a fine state of division to the

air, gradually becomes converted into brittle, resinous matter, very

similar to shell-lac.

{43} Fritz Muller informs me that he saw in the forests of South

Brazil numerous black strings, from some lines to nearly an inch in

diameter, winding spirally round the trunks of gigantic trees. At

first sight he thought that they were the stems of twining plants

which were thus ascending the trees: but he afterwards found that

they were the aerial roots of a Philodendron which grew on the

branches above. These roots therefore seem to be true twiners,

though they use their powers to descend, instead of to ascend like

twining plants. The aerial roots of some other species of

Philodendron hang vertically downwards, sometimes for a length of

more than fifty feet.

{44} Quoted by Cohn, in his remarkable memoir, "Contractile Gewebe

im Pflanzenreiche," 'Abhandl. der Schlesischen Gesell. 1861, Heft i.

s. 35.

{45} Such slight spontaneous movements, I now find, have been for

some time known to occur, for instance with the flower-stems of

Brassica napus and with the leaves of many plants: Sachs' 'Text-Book

of Botany' 1875, pp. 766, 785. Fritz Muller also has shown in

relation to our present subject ('Jenaischen Zeitschrift,' Bd. V.

Heft 2, p. 133) that the stems, whilst young, of an Alisma and of a

Linum are continually performing slight movements to all points of

the compass, like those of climbing plants.

{46} Mr. Herbert Spencer has recently argued ('Principles of

Biology,' 1865, p. 37 et seq.) with much force that there is no

fundamental distinction between the foliar and axial organs of

plants.

{47} Annales des Sc. Nat. 4th series, Bot. tom. vi. 1856, p. 31.

{48} Moquin-Tandon (Elements de Teratologie. 1841, p. 156) gives the

case of a monstrous bean, in which a case of compensation of this

nature was suddenly effected; for the leaves completely disappeared

and the stipules grew to an enormous size.

End of The Project Gutenberg Etext of Climbing Plants by Charles Darwin

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