02 of a grain (1.23 mg.) in weight, gently placed
on the concave point, caused a tendril to become hooked, as did a
loop of soft, thin cotton thread weighing one thirty-second of a
grain (2.02 mg.) With the tendrils of several other plants, loops
weighing one sixteenth of a grain (4.05 mg.) sufficed. The point of
a tendril of Passiflora gracilis began to move distinctly in 25
seconds after a touch, and in many cases after 30 seconds. Asa Gray
also saw movement in the tendrils of the Cucurbitaceous genus,
Sicyos, in 30 seconds. The tendrils of some other plants, when
lightly rubbed, moved in a few minutes; with Dicentra in half-an-
hour; with Smilax in an hour and a quarter or half; and with
Ampelopsis still more slowly. The curling movement consequent on a
single touch continues to increase for a considerable time, then
ceases; after a few hours the tendril uncurls itself, and is again
ready to act. When the tendrils of several kinds of plants were
caused to bend by extremely light weights suspended on them, they
seemed to grow accustomed to so slight a stimulus, and straightened
themselves, as if the loops had been removed. It makes no difference
what sort of object a tendril touches, with the remarkable exception
of other tendrils and drops of water, as was observed with the
extremely sensitive-tendrils of Passiflora gracilis and of the
Echinocystis.
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