Page:Darwin - On the movements and habits of climbing plants.djvu/45

 anticipated that so lowly a plant would have been a climber. This it effects by the aid of the main and lateral petioles of its compound leaves; even the much-flattened terminal portion of the petiole can seize a support. I have seen a substance as soft as a withered blade of grass caught. Petioles which have clasped any object ultimately became rather thicker and more cylindrical. On lightly rubbing with a twig several petioles, they became perceptibly curved in 1 h. 15 m., and subsequently they straightened themselves. A stick gently placed in the angle between two sub-petioles caused movement in 7 h., and was almost clasped in 9 h. A loop of thread, weighing one-eighth of a grain, caused, after 12 h. and before 20 h. had elapsed, a considerable curvature; but the petiole never fairly clasped the thread. The young internodes arc in continual movement; the movement is considerable, but very irregular in course; a zigzag line, or a spire crossing itself, or a figure of 8 is formed; the course during 12 h., being traced on a bell-glass, apparently represented about four ellipses. The leaves themselves also move spontaneously, the main petiole curving itself in accordance with the movement of the internodes; so that when the latter move to one side the petiole is curved to that side, then, becoming straight, is curved to the opposite side. Thus a wider space is swept for a support to be clasped. The movement, however, is small, as could be seen when the shoot was securely tied to a stick and the leaf alone allowed to move. The leaf in this case followed an irregular course, like that made by the young internodes.

Adlumia cirrhosa.—I raised some plants late in the summer; they formed magnificent leaves, but threw up no central stem. The first-formed leaves were not sensitive; but some of the later leaves were sensitive, but only towards their extremities, and were able to clasp sticks. This could be of no service to the plant, as these leaves rose from the ground; but it showed what the future character of the plant would be when it had grown tall enough to climb. The tip of one of these ground leaves, whilst young, described in 1 h. 36 m. a narrow ellipse, open at one end, and exactly three inches in length; a second ellipse was broader, more irregular, and shorter, viz. only 2½ inches in length, and was completed in 2 h. 2 m. From analogy with Fumaria and Corydalis, I have no doubt that the internodes have the power of revolving.