XLIL— GEO-ELECTRIC RESPONSE OF ROOT 



Bu 



Sir J. C. BosE, 



Assisted by 



Satyendra Chandra Guha. 



The effects of various stimuli, direct and indirect, on 

 the response of the root have been described in the last 

 chapter. These responsive reactions have been found to 

 be in no way different from those of the shoot. But the 

 shoot and the root exhibit under the stimulus of gravity, 

 responsive movements which are diametrically opposite to 

 each other. These opposite effects of an identical stimulus 

 have been regarded as due to specific differences of irrita- 

 bility in the two organs, specially evolved for the advantage 

 of the plant. The root is thus supposed to be charac- 

 terised by " positive " and the shoot by " negative " geotro- 

 pism. 



As regards r'esponse to other forms of stimuli, the root 

 has been shown to behave like the shoot. We have now 

 to inquire whether the reaction of the root to gravitational 

 stimulus is specifically different to that of the shoot. 



The electric method of investigation described in the 

 last chapter, holds out the possibility of discovering the 

 character of the responsive reaction induced in the root 

 by its displacement from vertical to horizontal position ; 

 we shall, moreover, be able to make an electrical explora- 

 tion of the root-tip and the zone of growth, and thus 

 determine the qualitative changes of response, induced 

 in two regions of the root under the action of gravitational 

 stimulus. For the detection of geotropic action in the shoot, 



