Page:Darwin - On the movements and habits of climbing plants.djvu/69

 foliar nature than most other tendrils, yet display all the ordinary characteristic movements, both those that are spontaneous and those 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, which evidently represent in a much elongated condition the petioles and midribs of three leaflets; for the branches of the tendril are exactly like the petioles and midribs of the leaflets, being square on the upper surface, furrowed, and edged with green. Moreover, in the plant whilst quite young, the green edging to the branches of the tendrils sometimes expands into narrow laminæ or blades. Each branch is curved a little downwards, and is slightly hooked at its extremity.

An upper young internode revolved, judging from three revolutions, at an average rate of 1 h. 38 m.; it swept ellipses with the longer axes directed at right angles to each other; the plant, apparently, cannot twine. The petiole which bears the tendril, and the tendril itself, are both in constant movement. But the movement is slower and much less regularly elliptical than that of the internodes; it is, apparently, much affected by the light, for the whole leaf usually sank during the night and rose during the day, moving in a crooked course to the west. The tips of the tendrils are highly sensitive on their lower surfaces: one just touched with a twig became perceptibly curved in 3 m., and another became so in 5 m.; the upper surface is not at all sensitive; the sides are moderately sensitive, so that two branches rubbed on their adjoining sides converged and crossed each other. The petiole of the leaf and the lower part of the tendril, halfway between the upper leaflet and the lowest tendril-branch, are not sensitive. A tendril after curling from a touch became straight again in about 6 h.,and was ready to react; but one that had been so roughly rubbed as to have coiled into a helix was not perfectly straight after 13 h. The tendrils retain their sensibility to an unusual age; for one borne by a leaf, with five or six fully developed leaves above it, was still active. If a tendril catches nothing, the tips of its branches, after a considerable interval of time, spontaneously curl a little inwards; but if the tendril has clasped some object, the whole length contracts spirally.

.—Smilax aspera, var. maculata.—Aug. St.-Hilaire considers the tendrils which rise in pairs from the petiole as