172 TfiNDEir^BEABEES. Chap. IV. 



a grain (4"05 mg.) sufficed. The point of a tendril of 

 Passiflora gracilis began to move distinctly in 25 

 seconds after a toucli, and in many cases after 30 

 seconds. Asa Gray also saw moyement 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 ten- 

 drils and drops of water, as was observed with the 

 extremely sensitive-tendrils of Passiflora gracilis and 

 of the Echinoeystis. 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 Cobaea 

 (though furnished with homy hooks directed to one side) 

 and those of Gissus discolor, are sensitive on all sides. 

 Hence the tendrils of this latter plant, when stimulated 



