INSECTIVOROUS AND CLIMBING PLANTS. 333 



parts act in climbing, the climbing and tlie growth are 

 entirely distinct. To this there is one exception — an 

 instructive one, as showing how one action passes into 

 another, and how the same result may be brought 

 about in different ways — that of stems which climb by 

 rootlets, such as of ivy and trumpet-creeper. Here the 

 stem ascends by growth alone, taking upward direc- 

 tion, and is fixed by rootlets as it grows. There is no 

 better way of climbing walls, precipices, and large 

 tree-trunks. 



But small stems and similar supports are best as- 

 cended by twining ; and this calls out powers of anoth- 

 er and higher order. The twining stem does not grow 

 around its support, but winds around it, and it does 

 this by a movement the nature of which is best ob- 

 served in stems which have not yet reached their sup- 

 port, or have overtopped it and stretched out beyond 

 it. Then it may be seen that the extending summit, 

 reaching farther and farther as it grows, is making free 

 circular sweeps, by night as well as by day, and irre- 

 spective of external circumstances, except that warmth 

 accelerates the movement, and that the general ten- 

 dency of young stems to bend toward the light may, 

 in case of lateral illumination, accelerate one-half the 

 circuit while it equally retards the other. The arrest 

 of the revolution where the supporting body is struck, 

 while the portion beyond continues its movement, 

 brings about the twining. As to the proximate cause 

 of this sweeping motion, a few simple experiments 

 prove that it results from the bowing or bending of the 

 free summit of the stem into a more or less horizontal 



position (this bending being successively to everv point 

 15 



