XL.— GEO-ELECTRIC RESPONSE OF SHOOT 



By 



Sir J. C. BosE, 



Assisted by 



Satyendra Chandra Guha, m.sc. 



The experiments that have been described in the pre- 

 ceding chapter show that the upper side of a horizontally 

 laid shoot undergoes excitatory contraction, in consequence 

 of which the organ bends upwards. The fundamental 

 geotropic reaction is, therefore, not expansion, but contrac- 

 tion which results from all modes of stimulation. 



In confirmation of the above, I wished to discover and 

 employ new means of detecting excitatory reaction under 

 geotropic stimulus. In regard to this, I would refer to the 

 fact which I have fully established that the state of excit- 

 ation can be detected by the induced electromotive change 

 of galvanometric negativity. This electrical indication of 

 excitation may be observed even in plants physically res- 

 trained from exhibiting response by mechanical movement.* 



ELECTRIC RESPONSE TO STIMULUS. 



Before giving account of the results of investigations 

 on the detection of geotropic excitation by means of 

 electric response, I shall describe a few typical experiments 

 which will fully explain the method of the electrical 

 investigation, and show the correspondence of mechanical 

 and electric responses. I have explained how tropic cur- 

 vatures are brought about by the joint effects, of 



* "Comparative Electro-Physiology." ]). 20. 



