The Rate of Revolution of various Twining Plants.

(Acotyledons.)

Lygodium scandens (Polypodiaceæ) moves against the sun.

Lygodium articulatum moves against the sun.

(Monocotyledons.)

Ruscus androgynus (Liliaceæ), placed in the hot-house, moves against the sun.

Asparagus (unnamed species from Kew) (Liliaceæ) moves against the sun, placed in hothouse.

Tamus communis (Dioscoreaceæ). A young shoot from a tuber in a pot placed in the greenhouse: follows the sun.

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

Roxburghia viridiflora (Roxburghiaceæ) moves against the sun; it completed a circle in about 24 hours.

(Dicotyledons.)

Humulus Lupulus (Urticaceæ) follows the sun. The plant was kept in a room during warm weather.

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.

Stauntonia latifolia (Lardizabalaceæ), placed in hothouse, moves against the sun.

Sphærostemma marmoratum (Schizandraceæ) follows the sun.

Stephania rotunda (Menispermaceæ) moves against the sun.

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.

Hibbertia dentata (Dilleniaceæ), 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 (Pittosporaceæ) moves against the sun kept in greenhouse.

Polygonum dumetorum (Polygonaceæ). 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 (Leguminosæ), in greenhouse, moves against the sun.

Phaseolus vulgaris (Leguminosæ), in greenhouse, moves against the sun.

Dipladenia urophylla (Apocynaceæ) moves against the sun.

Dipladenia crassinoda moves against the sun.

Ceropegia Gardnerii (Asclepiadaceæ) moves against the sun.

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.

Ipomæa jucunda (Convolvulaceæ) moves against the sun, placed in my study, with windows facing the north-east. Weather hot.

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.

Tecoma jasminoides (Bignoniaceæ) moves against the sun.

Thunbergia alata (Acanthaceæ) moves against sun.

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.

Combretum argenteum (Combretaceæ) moves against the sun. Kept in hothouse.

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

Loasa aurantiaca (Loasaceæ). Revolutions variable in their course: a plant which moved against the sun.

Another plant which followed the sun in its revolutions.

Scyphanthus elegans (Loasaceæ) follows the sun.

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

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

Lonicera brachypoda (Caprifoliaceæ) follows the sun, kept in a warm room in the house.

Aristolochia gigas (Aristolochiaceæ) moves against the sun.

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.