STIMULATION OF ROOT I43 



unilateral stimulation of the tip of the shoot, when the tip 

 happened to be at a certain distance from the region of active 

 growth. The final result is somewhat dependent on the 

 conducting power of the intervening length of tissue. In 

 cases where the tissue is highly conducting, the excitatory 

 negative impulse, reaching the growing region, induces a 

 positive curvature. 



Effect of Simultaneous Stimulation of the Tip 

 AND OF the Growing Region of Root 



When the growing region of the root is directly stimu- 

 lated by unilateral light, the response is a positive curva- 



FiG. 81. Effect of simultaneous unilateral stimulation 

 of the tip and of the growing region of root (Ipomoea). 



Successive dots at intervals of 10 seconds. 



ture in contrast with the negative curvature induced 

 by indirect stimulation {cf. also Experiment 86). I next 

 observed the effect of simultaneous direct and indirect 

 unilateral stimulation of the root. 



