SUMMARY 325 



The mean ratio 1-49 may thus be regarded as that 



of the geotropic reactions at 90° and 45°; this is practically 



. sin 00° ... 



the same as -r— — 5 = 1-4, which may be stated as the 

 sm 45 ^ -^ 



following law : 



The intensity of geotropic reaction varies as the sine of the 

 directive angle. 



The results obtained with the Method of Vertical Rota- 

 tion will be described in a subsequent chapter. 



Summary 



The excitatory response to geotropic stimulation has 

 been discovered by the electrical method, the sign of ex- 

 citation being an electromotive change of galvanometric 

 negativity. 



In addition to the method of contact with an indifferent 

 point, two other methods have been rendered practical, 

 the methods of Axial and of Vertical Rotation. The upper 

 side of a horizontally laid shoot is found to undergo an 

 excitatory change of galvanometric negativity. 



In quickly reacting organs the latent period of geo- 

 electric response is about 5 seconds, and the maximum 

 excitation is induced in the course of less than 2 minutes. 



Under symmetrical conditions the intensity of geotropic 

 reaction is found to be proportional to the sine of the angle 

 of inclination. 



