^74 



LIFE MOVEMENTS IN PLANTS 



In any case it is important to remember the following 

 characteristic effects of indirect stimulation. 



TAULE XXn. — SHOniNG THE EFKECT OF INDIKECT STIMULATION. 



These effects of indirect stimulation have been fully 

 demonstrated in the case of pulvinated organs (p. 136) and 

 growing organs (p. 215). 



Having demonstrated the fundamental reactions of 



direct and indirect stimulation, we shall next study the 



tropic effects induced in growing organs by the effect of 

 unilateral application of indirect stimulus. 



Experiment 108. — I have already explained, how thermal 

 radiation is almost as effective in inducing contraction 

 and retardation of growth as th3 more refrangible rays 

 of the spectrum. The thermal radiation was produced by 

 the heating of a platinum spiral, short of incandescence, 

 by the passage of an electric current. The intensity of 

 radiation is easily varied by adjustment of the current by 

 means of a rheostat. The experimental specimen was a 

 flower bud of Crinum. It was held by a clamp, a little 

 below the region of growth. Stimulus was applied below 

 the clamp so that the transmitted effect had to pass 



