02 CHAP. X. EFFECT OF MECHANICAL STIMULATION 



indications of which give the immediate and the after-effect 

 of stimulation. After securing exact balance, the record was 

 horizontal. Indirect stimulation w^as now appHed below 



the clamp ; this upset the 

 balance, show^n by the 

 resulting up-curve, which 

 indicates a sudden acceler- 

 ation of growth above the 

 normal. This acceleration 

 took place within lo 

 seconds of the application 

 of stimulus and persisted 

 for 3 minutes. The normal 

 rate of growth then be- 

 came restored, the record 

 becoming once more hori- 

 zontal (fig. 45). 



Experiment 53. Effect 

 of direct electric stimula- 

 tion.- — The contraction 

 induced by direct stimu- 

 lation is so great that the 

 record obtained by the sen- 

 sitive method of balance 

 cannot be kept within the 

 plate. I therefore took 

 a Crescographic record of 

 the growlh-curve without 

 balance. The first part 

 of the curve represents 

 normal grow^th; stimulus 

 of a feeble electric current 

 w^as then directly applied 

 near the highest point of the curve. This induced an 

 immediate contraction *and reversal of the curve, the 

 contraction persisting for 2 J minutes ; growth w^as then 

 slowly renewed (fig. 46). The most interesting fact re- 

 garding the after-effect of stimulation is that the rate of 



Fig. 46. Variation of growth of tendril 

 induced by direct electric stimulation. 



First part of the curve shows normal 

 rate of growth. Direct stimulation 

 induced contraction (reversal of 

 curve). After-effect of stimulation 

 seen in highly erect curve in upper 

 part of record, taken after 20 minutes 

 (Cucurbita). 



