XLIIL— LOCALISATION OF GEO-PERCEPTIVE LAYER 



BY MEANS OF THE ELECTRIC PROBE 



By 



Sir J. C. BoSE, 



Assisted by 



Satyendra Chandra Guha. 



The obscurities which surround the phenomenon of 

 geotropism arise : (1) from the invisibility of the stimulating 

 agent, (2) from want of definite knowledge as to whether 

 the fundamental reaction is contractile or expansive, and 

 (3) from the peculiar characteristic that the stimulus is only 

 effective when the exter?ial force of gravity reacts internally 

 through the mass of contents of the sensitive cells. 



The experiments that have been detailed in the foregoing 

 chapters will have removed most of the difficulties. But 

 beyond these is the question of that power possessed 

 by plants of jjerxeiving geotropic stimulus by means of 

 certain localised sense organs, which send out impulses in 

 response to which neighbouring cells carry out the move- 

 ment of orientation in a definite direction. Are the sensi- 

 tive cells diffusely distributed in the organ or do they form 

 a definite layer ? Could we by the well established method 

 of physiological response localise the sensitive cells in the 

 interior of the organ ? As the internal cells are not acces- 

 sible, the problem would appear to be beyond the reach of 

 experimental investigation. 



It is true that post-mortem examination of sectioned 

 tissues undei- the microscope enables us to form a probable 

 hypothesis as regards the conieuts of certain cells causing 

 geotropic irritation ; we have thus the very illuminating 



