SUMMARY 69 



growth-elongation is represented as a down-curve. On the 

 apphcation of stimulus, the normal expansion was suddenly 

 reversed to excitatory contraction ; the latent period was 

 I second, and the period of attainment of maximum con- 

 traction 4 minutes. The organ 

 recovered its original length 

 after a period of 7 minutes. 

 Repeated stimulation gave rise 

 to repeated responses as in the 

 case of Mimosa. 



Arbitrary Distinction be- 

 tween Responses of Pulvi- 

 NATED and Growing Organs 



The growing organ, when 

 subjected to successive stimu- 

 lations, gives a contractile 

 response in every way similar 

 to the mechanical response of 

 Mimosa. An arbitrary dis- 

 tinction has been drawn be- 

 tween the response of pulvinated and that of growing organs. 

 The movement of the former has been distinguished as 

 one of variation adapted for repetition an infinite number 

 of times, w^hereas a growing organ has been supposed to be 

 incapable of exhibiting repeated response. The experiment 

 described proves that there is no such basic distinction 

 between the two classes of phenomena. 



Fig. 32. Contractile response of 

 a growing organ under electric 

 shock (Crinum). 



Successive dots at intervals of 4 

 seconds. Vertical lines below 

 represent intervals of i minute. 

 (Magnification 1000 times.) 



Summary 



In normal conditions, electric stimulation induces incipient 

 contraction exhibited by retardation of the rate of growth. 

 Growth may be affected by an intensity of stimulation 

 below the range of human perception. 



