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- CLIMBING PLANTS - 5/27 -


{ 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


CLIMBING PLANTS - 5/27

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