CHAPTER XXXI 



RELATION BETWEEN ANGLE OF INCLINATION AND 

 GEOTROPIC EXCITATION 



If the pressure of heavy particles on the sensitive ecto- 



plasmic layer of the cell be the efficient cause of stimulation 



by gravity, it would follow that the excitation caused by 



them will increase with the angle of inclination. The 



following experiments were carried out by the Method of 



Vertical Rotation, the effect of which is somewhat different 



from that of Axial Rotation described in a previous chapter. 



There is no effective stimulation in the vertical position of 



the plant, while it is most intense at an inclination of 90°. 



The effective pressure on the protoplasm of the perceptive 



cell which stimulates it, will evidently increase with the angle 



of inchnation to the vertical. The problem to be solved is 



the exact determination of the relation between the angle 



of inclination and the associated excitation. 



As regards the measurement of the induced excitatory 

 reaction, it is theoretically possible to determine it from either 

 mechanical or the electric response at various inclinations. 

 The practical difficulties in the measurement of the mechanical 

 response are, however, so numerous, that it is impossible 

 to obtain with it any sufficiently accurate result. No such 

 difficulties are encountered in the electric method, the 

 relative advantages of which are as foUows : 



I. The latent period is very short and the maximum 

 excitatory reaction is attained in the course of 

 a minute or so ; 



