Six wind-vanes could not
have more truly shown the direction of the wind, than did these
branched tendrils the course of the stream of light which entered the
box. I left these tendrils undisturbed for above 24 hrs., and then
turned the pot half round; but they had now lost their power of
movement, and could not any longer avoid the light.
When a tendril has not succeeded in clasping a support, either
through its own revolving movement or that of the shoot, or by
turning towards any object which intercepts the light, 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 seizes an object, all the branches contract
spirally.
I have stated that after a tendril has come into contact with a
stick, it bends round it in about half an hour; but I repeatedly
observed, as in the case of B. speciosa and its allies, that it often
again loosed the stick; sometimes seizing and loosing 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
from these objects with what I can only call disgust, and
straightened themselves.
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