Page:Darwin - On the movements and habits of climbing plants.djvu/85

 examining this plant, I had observed only those tendrils which are sensitive on one side, and these when lightly pressed between the finger and thumb become curved; but on thus pinching many times the tendrils of this Cissus no curvature ensued, and I was at first falsely led to infer that they were not at all sensitive to a touch.

Cissus antarcticus.—The tendrils on a young plant were thick and straight, with the tips a little curved; when the concave surface was rubbed with some force they very slowly became curved, and subsequently became straight again. Hence they are much less sensitive than the tendrils of the last species; but they made two revolutions, following the sun, rather more rapidly, viz. in 3 h. 30 m. and 4 h. The internodes do not revolve.

Ampelopsis hederacea, or Virginian Creeper.—In this plant also the internodes do not move more than apparently can he accounted for by the varying action of the light. The tendrils are from 4 to 5 inches in length; the main stem sends off several lateral branches, which have their tips curved, as may be seen in fig. 11, A. They exhibit no true spontaneous revolving movement, but turn, as was long ago observed by Andrew Knight, from the light to the dark. I have seen several tendrils move through an angle of 180° to the dark side of a case in less than 24 hours; but the movement is sometimes very much slower. The several lateral branches often move independently of each other, 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 rubbings 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 crawled over a large box-tree clasped several of the branches. But I have repeatedly seen the tendrils come into contact with sticks, and then withdraw from them. 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