Page:Darwin - On the movements and habits of climbing plants.djvu/75

 Echinocystis lobata.—I made numerous observations on this plant (raised from seed sent me by Prof. Asa Gray), for here I first observed the spontaneous revolving movement of the internodes and of the tendrils; and knowing nothing of the nature of these movements, was infinitely perplexed by the whole case, and by the false appearance of twisting of the axis. My observations may now be greatly condensed. I recorded thirty-five revolutions of the internodes and tendrils; the slowest rate was 2 h., and the average, with no great fluctuations, was 1 h. 40 m. for each revolution. Sometimes I tied the internodes, so that the tendrils alone moved; at other times I cut off the tendrils whilst very young, so that the internodes revolved by themselves; but the rate was not thus affected. The course generally pursued was with the sun, but often in the opposite direction; sometimes the movement during a short time would either stop or be reversed; and this apparently resulted from the interference of the light, shortly after the plant was placed close to a window. In one instance, an old tendril, which had nearly ceased revolving, moved in one direction, whilst the young tendril above moved in the opposite direction. The two uppermost internodes alone revolve; as the internodes grow old, the upper part alone moves. The summit of the upper internode made an ellipse or circle about 3 inches in diameter, whilst the tip of the tendril swept a circle 15 or 16 inches in diameter. During the revolving movement the internodes become successively curved to all points of the compass; and often in one part of their course they were inclined, together with the tendril, at about 45° to the horizon, and in another part stood vertical. There was something in the appearance of the revolving internodes which continually gave the false impression that their movement was due to the weight of the long and spontaneously revolving tendril; but, on suddenly cutting off the tendril with a sharp scissors, the top of the shoot rose very little, and went on revolving: this false appearance is apparently due to the internodes and tendrils all curving and moving harmoniously together.

I repeatedly saw that the revolving tendril, though inclined during the greater part of its course at an angle of about 45° (in one case of only 37°) above the horizon, in one part of its course stiffened and straightened itself from tip to base, and became