132 TENDKIL-BEAEEKS. Chap. IV. 



a half ; but in one case, in wliich a tendril depended at 

 an angle of 45° beneath the horizon, the uprising took 

 two hours ; in half an hour afterwards it rose to 23° 

 above the horizon and then recommenced reTolving. 

 This upward movement is independent of the action of 

 light, for it occurred twice in the dark, and on another 

 occasion the light came in on one side alone. The 

 movement no doubt is guided by opposition to the 

 force of gravity, as in the case of the ascent of the 

 plumules of germinating seeds. 



A tendril does not long retain its revolving power; 

 and as soon as this is lost, it bends downwards and 

 contracts spirally. After the revolving movement 

 has ceased, the tip still retains for a short time its 

 sensitiveness to contact, but this can be of little or no 

 use to the plant. 



Though the tendril is highly flexible, and though 

 the extremity travels, under favourable circumstances, 

 at about the rate of an inch in two minutes and a 

 quarter, yet its sensitiveness to contact is so great that 

 it hardly ever fails to seize a thin stick placed in its 

 path. The following case surprised me much : I placed 

 a thin, smooth, cylindrical stick (and I repeated the 

 experiment seven times) so far from a tendril, that 

 its extremity could only curl half or three-quarters 

 round the stick; but I always found that the tip 

 managed in the course of a few hours to curl twice 

 or even thrice round the stick. I at first thought 

 that this was due to rapid growth on the outside ; but 

 by coloured points and measurements I proved that 



