172 TENDRIL-BEARERS. Cuar. IV. 
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 Cueurbitaceous genus, Stcyos, 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 ten- 
drils and drops of water, as was observed with the 
extremely sensitive-tendrils of Passiflora gracilis and 
of the LEchinocystis. I have, however, seen tendrils 
of the Bryony which had temporarily caught other 
tendrils, and often in the case of the vine. 
Tendrils of which the extremities are permanently 
and slightly curved, are sensitive only on the concave 
surface; other tendrils, such as those of the Cobwxa 
(though furnished with horny hooks directed to one side) 
and those of Cissus discolor, are sensitive on all sides. 
Hence the tendrils of this latter plant, when stimulated 
