APTEll-EFFECT OF LIGHT 571 



experiments at «, b, and c (Fig. 106). Continuous stimu- 

 lation induces increasing galvanoraetric negativity ; when 



Fig. 205. Fig. ?06. 



Fiu. 205. — Electric response of the leaf-stalk of Bryophylliim under continuous 

 photic .stimulation. Increasing negativitj' represented by up-curve. neutralisation 

 by down-curve. 



Fig. 206. — Diagrammatic representation of electric after-effect of stimulation. 

 Pre-maximal stimulation produced by stoppage of light at a, gives rise to continua- 

 tion of previous response followed by recovery. Stoppage of light at maximum 6 

 gives rise to recovery to equilibrium position. Stoppage of light at post-maximum 

 c, gives rise to over-shooting below zero line. 



stimulus is stopped at a before the maximum, the after- 

 effect is a persistence of excitatory galvanometric negativity, 



