The Movements and Habits of Climbing Plants · Charles Darwin
(DICOTYLEDONS.)
_Humulus Lupulus_ (Urticaceæ) 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_ (Lardizabalaceæ), 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_ (Lardizabalaceæ), placed in hothouse, moves against the sun. H. M. March 28, 1st circle was made in 3 30 29, 2nd 3 45 _Sphærostemma marmoratum_ (Schizandraceæ) 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_ (Menispermaceæ) 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 (Malpighiaceæ) 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.
_Dipladenia urophylla_ (Apocynaceæ) 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_ (Asclepiadaceæ) moves against the sun. H. M. Shoot very young, 2 inches in 1st circle was 7 55 length performed in Shoot still young 2nd 7 0 Long shoot 3rd 6 33 Long shoot 4th 5 15 Long shoot 5th 6 45 _Stephanotis floribunda_ (Asclepiadaceæ) moves against the sun and made a circle in 6 hrs. 40 m., a second circle in about 9 hrs. _Hoya carnosa_ (Asclepiadaceæ) made several circles in from 16 hrs. to 22 hrs. or 24 hrs. _Ipomæa purpurea_ (Convolvulaceæ) moves against the sun. Plant placed in room with lateral light. 1st circle was made in 2 hrs. 42 Semicircle, from the light in 1 m. hr. 14 m., to the light 1 hr. 28 m.: difference 14 m. 2nd circle was made in 2 hrs. 47 Semicircle, from the light in 1 m. hr. 17 m., to the light 1 hr. 30 m.: difference 13 m. _Ipomæa jucunda_ (Convolvulaceæ) moves against the sun, placed in my study, with windows facing the north-east. Weather hot.
1st circle was made in 5 hrs. 30 Semicircle, from the light in 4 m. hrs. 30 m., to the light 1 hr. 0 m.: difference 3 hrs. 30 m. 2nd circle was made in 5 hrs. 20 Semicircle, from the light in 3 m. (Late in afternoon: circle hrs. 50 m., to the light 1 hr. 30 completed at 6 hrs. 40 m. P.M.) m.: difference 2 hrs. 20 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 tiliæfolia_ (Convolvulaceæ) 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_ (Plumbaginaceæ) 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 (Jasminaceæ), moves against the sun. A circle was made in 7 hrs. 15 m., and a second rather more quickly. _Clerodendrum Thomsonii_ (Verbenaceæ) follows the sun. H. M. April 12, 1st circle was made in 5 45 (shoot very young) 14, 2nd 3 30 18, a semicircle 5 0 (directly after the plant was shaken on being moved) 19, 3rd circle 3 0 20, 4th 4 20 _Tecoma jasminoides_ (Bignoniaceæ) 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_ (Acanthaceæ) 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 cydonæfolia_ (Acanthaceæ) 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_ (Compositæ) 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 watering with cold water at 47° Fahr.
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 Leguminosæ, and we have in the table another in the Acanthaceæ. I have seen no instance of two species of the same genus twining in opposite directions, and such cases must be rare; but Fritz Müller {33} 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_ (Léon, 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, {34} 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; {36} 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 4½ 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 Menispermaceæ, and with some Dalbergias and other Leguminosæ. {37} 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 _Sphærostemma 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 Græca_ (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 Asclepiadaceæ 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 Convolvulaceæ are excellent twiners; but in South Africa _Ipomoea argyræoides_ 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 (Léon, 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.
Text from Project Gutenberg, public domain in the United States.