CHAPTER IX 



ACCELERATION OF GROWTH IN SUBTONIC PLANTS ON 



STIMULATION 



A ITER investigation of the normal effect of electric and 

 photic stimulation in retarding growth, described in the two 

 previous chapters, it was a matter of considerable surprise 

 to me that the responses were occasionally positive ; that 

 is to say, an acceleration of growth instead of the normal 

 negative response of retardation. After giving an account 

 of these positive responses, I shall attempt to trace the 

 cause of the abnormahty. 



Acceleration of Growth under Light 



Experiment 46.— The specimen employed was Kysoor, 

 which was exposed to the action of strong hght for 5 minutes. 

 Its normal rate of growth was 0-3 [j. per second ; but after 

 exposure to light there was an enhancement of the rate of 

 growth to 0-40 tjL per second. 



The plant was then subjected to the continued action 

 of light for half an hour, which caused a transformation of 

 the response from the abnormal positive acceleration to the 

 normal negative retardation of growth. The question now 

 arises : What is the characteristic of the organ which pre- 

 disposed it to give a positive response, and how did the 

 positive response at the beginning become transformed into 

 the normal negative under the continued action of light ? 



Referring to fig. 33 (p. 72), in which normal retardation 

 of growth occurred in Kysoor, it was found that its rate of 

 growth was as high as o-8 [x per second. But in Experi- 

 ment 46, in which there was an acceleration of growth 



