

INDIRECT STIMULATION 



399 



becomes maximal after a certain duration of application. 

 This explains the most frequently observed effect of stimu- 

 lation — namely, a preliminary increase followed by a 

 diminution in the rate of torsion. 



Effect of Indirect Stimulation 



Another important result which I have obtained is the 

 effect of indirect stimulation on growth. Stimulation is 

 said to be indirect when it is applied at some distance from 

 the responding growing region. I have been able to estab- 

 lish the generalisation (p. 131) that while direct stimulation 

 induces retardation, indirect stimulation causes enhance- 

 ment, of the rate of growth. 



The effect of indirect stimulation on autonomous 

 torsion proves to be an increase in the rate of movement. 

 Stimulation was effected indirectly by application of electric 

 shock for 4 minutes to the cut stem below the clamp which 

 supported it. 



Experiment 216. — The specimen employed was Thun- 

 bergia, the normal rate being 8. As the result of indirect 

 stimulation, the rate was increased to a maximum of 95 

 in the course of 6 minutes. The rate was restored to nearly 

 the normal in the course of 40 minutes. Other examples are 

 given in the following table : 



Table XLIX. — Effect of Indirect Stimulation in Enhancing 



THE Rate of Torsion. 



Effect of Thermal Shock 



It may be said in general that any sudden variation of 

 external conditions constitutes a stimulus. Electric stimu- 

 lation by an induction current is due to abrupt change of 



