MINIMAL STIMULATION 397 



The following table gives typical results obtained with 

 different plants : 



Table XLVI. — Effect of Strong Electric Stimulation on 



Torsional Response. 



The results given in previous chapters have established 

 the generalisation that all forms of maximal stimulation — ■ 

 electric, mechanical, or photic — induce a retardation of 

 the rate of growth ; that under increasing intensity or 

 duration of the stimulus the retardation culminates in an 

 actual contraction (p. 67) . On this principle, it is retardation 

 of the rate of growth and contraction of the more active 

 half of the differentially growing stem that cause the dimi- 

 nution in the rate of torsion, culminating in actual reversal 

 of direction, which follows strong stimulation. 



Effect of Minimal Stimulation 



In investigations on growth, I found that while a 

 strong stimulus induces retardation, a feeble stimulus 

 causes enhancement of the rate of growth. In the range 

 of stimulation between minimal and maximal there is a 

 critical intensity, above which there is retardation, and 

 below which there is acceleration. The critical point is 

 modified by the tonic condition of the organ, being rela- 

 tively high in a subtonic specimen. It is therefore easier 

 to obtain the enhancement of the rate of growth under 

 stimulation in subtonic specimens. I found, moreover, that 

 in such specimens the tonicity is improved by the stimula- 

 tion, as manifested by a permanent increase in the rate of 

 growth. In torsional response the rate of normal movement 



