WOUND 



89 



Effect of Wound 



A prick causes an intense excitation in Mimosa ; I 

 tried the effect of this form of stimulation on a growing 

 organ. 



Experiment 51. — The specimen was the same as had 

 been employed in the last experiment. After moderate 

 stimulation by friction it had, in the course of an hour, 

 completely recovered its normal rate of growth of o-i8 y. 

 per second. The stimulus of a pin-prick was now applied ; 

 the actual injury to the tissue was relatively slight, but the 

 retardation of growth induced by this relatively intense 

 stimulation was very great. With moderate mechanical 

 friction the rate had fallen from • 18 [j, to • 11 [j. per second, 

 i.e. to three-fifths the normal rate ; but the prick induced 

 a depression of growth from o-i8 ^ to 0-05 [i per second, 

 i.e. to less than a third of the normal rate. After 15 minutes 

 the rate recovered from 0-05 11 to o -o? u- per second. After 

 moderate friction the recovery was completed after an 

 hour ; but after the prick the recovery at the end of an 

 hour was onl}^ three-fourths of the normal, the rate being 

 now 0-12 [jl per second (fig. 43). I next applied the more 

 intense stimuation • induced by a longitudinal cut. This 

 caused a depression of the growth-rate to 0-04 a per 

 second. A transverse cut was found to be far more effec- 

 tive in retarding growth than a longitudinal slit. 



Table XI. — Effect of Mechanical Stimulation and of Wound 



ON Growth (Zephyranthes). 



