TRANSMITTED EFFECT OF LIGHT 377 



negative). The final result is thus a movement away 

 from light or a negative phototropic curvature. 



SUMMARY. 



The effect induced by stimulus of light is transmitted 

 to a distance, in a manner precisely the same as in 

 other modes of stimulation. 



In the Paniceae, the local unilateral stimulation of the 

 tip of the cotyledon induces positive curvature in the 

 growing hypocotyl, at some distance from the tip. This is 

 due to transmitted excitatory effect- of indirect stimulation ; 

 the earlier positive impulse induces a })reliminary negative 

 curvature, which is reversed later by the excitatory negative 

 impulse into positive curvature. 



Contrary lo generally accepted view the hypocotyl not 

 only perceives but responds to light. The positive curva- 

 ture induced by direct stimulation is, however, neutralised 

 by transverse conduction of excitation. 



The effects of direct and indirect stimulus are inde- 

 pendent of each other ; the final effect is determined by 

 their algebraical suniuiation. 



29 A 



