Page:Darwin - On the movements and habits of climbing plants.djvu/53

 in comparison with those of the previous species. The lower part, or tarsus, is four times as long as the three toes; these are of equal length; they do not lie in the same plane, but diverge equally on all sides; their tips are bluntly hooked, so that the whole tendril makes an excellent grapnel. The tarsus is sensitive on all sides; but the three toes are sensitive only on their outer surfaces, which correspond with the under surfaces of the toes in the tendrils of the previous species. The sensitiveness is not much developed; for a slight rubbing with a twig did not cause the tarsus or toes to become slightly curved until an hour had elapsed; subsequently they straightened themselves. Both tarsus and toes can seize well hold of sticks. When the stem is secured, the tendrils are seen spontaneously to sweep large ellipses: the two opposite tendrils move independently of each other. I have no doubt, from the analogy of the two following allied species, that the petioles move spontaneously; but they are not irritable like those of B. unguis and B. Tweedyana. The young internodes also sweep fine large circles, one being completed in 2 h. 15 m., and a second in 2 h. 55 m. By these combined movements of the internodes, petioles, and grapnel-like tendrils, the latter are soon brought into contact with surrounding objects. When a shoot stands near an upright stick, it twines regularly and spirally round it; as it ascends, it seizes the stick with only one of its tendrils, and, if the stick be thin, the right- and left-hand tendrils are alternately used. This alternation follows from the stem necessarily taking one twist round its own axis for each completed spire.

The tendrils a short time after catching any object contract spirally. Those which have caught nothing slowly bend downwards, but do not contract spirally. With many plants the tendrils after a time contract spirally, whether or not they have caught any object. But this whole subject of the spiral contraction of tendrils will be discussed after the several tendril-bearing plants have been described.

Bignonia littoralis.—The young internodes revolve in fine large ellipses. An internode bearing immature tendrils made two revolutions, each in 3 h. 50 m.; but when grown older, with the tendrils mature, two ellipses were performed, each at the rate of 2 h. 44 m. But this species, unlike the preceding, is incapable of spirally twining round any object: this did not appear due to any want of flexibility in the internodes, or to the action of the tendrils, and certainly not to any want of the revolving power; nor can I