GEO-ELECTRIC RESPONSE OF ROOT 477 



The electric response in the growing region above the 

 stimulated point of the root-tip is positive, indicative of 

 increase of turgor and expansion. This is due to the effect 

 of indirect stimulus. 



The stimulus of gravity is perceived at the root-tip ; 

 it is the effect of indirect stimulus that is transmitted to 

 the responding region of growth. 



In contrast with the above is the fact that the growing 

 region of the shoot is both sensitive and responsive to 

 geotropic stimulus. 



As the effects of direct and indirect stimulation on 

 growth are antithetic, the responses of shoot and root to 

 the direct and indirect stimulus must be of opposite 

 signs. 



There is no necessity for postulating two different irri- 

 tabilities for the shoot and the root, since tis-iues in general 

 exhibit positive or negative curvatures according as the 

 stimulus is direct or indirect. 



