GEO-ELECTRIC RESPONSE OF SHOOT 



443 



contraction of the directly excited proximal side A, and the 

 expansion of the distal side B. In the diagram of mechanical 

 response to stimulus (Fig. 164a) the excitatory contraction 

 is indicated by - sign, and the expansion, by + sign. 

 The resulting movement is, therefore, towards the stimulus 

 as shown by the curved arrow. 



I shall now describe the corresponding electric eifects 

 in response to unilateral stimulus. We have to determine 

 the induced electrical variation at the proximal side A, 

 and at the distal side B. 



Electric response to direct stimulation : Experiment 168. — 

 For the determination of electric response at the directly excited 

 proximal side A, we take a shoot with a lateral leaf. The 

 point A, which is to undergo stimulation, is connected with 



Fig. 164. — Diagrammatic representation of the mechanical and electrical response 

 to direct unilateral stimulation indicated by arrow : — 



(a) Positive mechanical response (curved arrow) due to contraction of directly 



stimulated A, and expansion of indirectly stimulated B. 

 (6) Electric response of induced galvanometric negativity of A under direct 

 stimulation 



(c) Electric response of induced galvanometric positivity at the distal point 



B. 



(d) Additive effects of direct and indirect stimulations ; galvanometric nega- 



tivity of the directly stimulated proximal A, and galvanometric positivitv 

 of the indirectly stimulated distal point B. 



one terminal of the galvanometer, the other terminal being 

 led to an indifferent or neutral point N on the leaf. 



