444 



LIFE MOVEMENTS IN PLANTS 



Application of any form stimulus at A, gives rise to an 

 electric current which flows through the galvanometer from 

 the neutral to the excited point A (Fig. 164b). The directly 

 stimulated point A thus becomes galvanometricalli) negative. 

 The " action " current lasts during the application of stimulus 

 and disappears on its cessation. 



Electric response to indirect stimulation : Experimerd 

 169. — We have also seen that application of stimulus at A 

 causes indirect stimulation of the distal point B result- 

 ing in an increase of turgor and expansion. The corres- 

 ponding electric change of the indirectly stimulated point 

 B is found in the responsive current, which flows now 

 through the galvanometer from the indirectly stimulated B 

 to the, neutral point N (Fig. 164c). The indirectly stimu- 

 lated j^oint thus becomes galvanometrically positive. 



Having thus obtained the separate efl^ects at A and B, 

 we next modify the experiment for obtaining the joint 

 eff'ects. For this purpose the neutral point N is discarded 

 and A and B connected directly with the indicating gal- 

 vanometer. On stimulation of A that point becomes negative 

 and B positive, and the current of response flows through 

 the galvanometer from B to A. The deflection is increased 

 by the joint electrical reactions at A and B (Fig. 164d). 



The results may thus be summarised : — 



TABI.K XXXUI. — ELECTRIC RESPONSE TO DIRECT UNILATERAL STIMULUS. 



Electrical change at the proximal 

 side A. 



Galvanoinotric negativity indicative 

 of contraction and diminution 

 of turgor. 



Electrical change at the distal 

 side B. 



Galvanometric positivity indicative 



of expansion and increase of 



turgor. 



The corresponding tropic curvature is positive movement towards 

 stimulus. 



