I08 CHAP. XI. PHOTOTROPIC EFFECT OF LIGHT 



After the retardation, which lasted for lOO seconds, there 

 was an acceleration of growth above the normal, persist- 

 ing for 5 minutes, after which the rate of growth returned 

 to normal (fig. 55). 



Fig. od- Effect of a single electric spark in causing variation of 



growth. 



Record taken by Balanced Crescograph. Spark at arrow in- 

 duced retardation of rate (up-curve) ; after-effect is accelera- 

 tion above normal (dowoi- curve) followed by return to 

 normal rate. (Wheat.) 



In order to show that the induced variation is due to 

 the action of hght and not to any electric disturbance, I inter- 

 posed a sheet of ebonite between the spark-gap and the 

 plant ; there was now no response when the spark passed. 



Maximum Positive Curvature under Continued 



Action of Light 



One important factor in the production of positive 

 curvature is the contraction of the proximal side of the 

 organ. The curvature becomes greater and greater with 

 increasing contraction of that side. A limit of curvature 

 is, however, reached because : 



