Page:Darwin - On the movements and habits of climbing plants.djvu/58

 the light and the other to the darkest side of the house; the latter did not move, but the opposite one bent itself first upwards and then right over its fellow, so that the two became parallel, one above the other, both pointing to the dark: I then turned the plant half round; and the tendril which had turned over recovered its original position, and the opposite one, which had not moved before, now turned right over to the dark side. Lastly, on another plant, three pairs of tendrils were produced by three shoots at the same time, and all happened to be differently directed: I placed the pot in a box open only on one side, and obliquely facing the light; in two days all six tendrils pointed with unerring truth to the darkest corner of the box, though to do this each had to bend in a different manner. Six tattered flags could not have pointed more truly from the wind than did these branched tendrils from the stream of light which entered the box. I left these tendrils undisturbed for above 24 h., and then turned the pot half round; but they had now lost the power of movement, so that they could not any longer avoid the light.

When a tendril has not succeeded, either through its own revolving movement or that of the shoot, or by turning towards any object which intercepts the light, in clasping a support, it bends vertically downwards and then towards its own stem, which it seizes together with the supporting stick, if there be one. A little aid is thus given in keeping the stem secure. If the tendril seizes nothing, it does not contract spirally, but soon withers away and drops off. If it does seize an object, all its branches contract spirally.

I have stated that, after a tendril has come into contact with a stick, in about half an hour it bends round it; but I repeatedly observed, as with B. speciosa and its allies, that it again loosed the stick: sometimes it seized and loosed the same stick three or four times. Knowing that the tendrils avoided the light, I gave them a glass tube blackened within, and a well-blackened zinc plate: the branches curled round the tube and abruptly bent themselves round the edges of the zinc plate; but they soon recoiled, with what I can only call disgust, from these objects, and straightened themselves. I then placed close to a pair of tendrils a post with extremely rugged bark; twice the tendrils touched it for an hour or two, and twice they withdrew; at last one of the hooked extremities curled round and firmly seized an excessively minute projecting point of bark, and then the other branches spread