572 LIFE MOVEMENTS IN PLANTS 



which carries the response record higher up ; after a 

 certain interval recovery takes place and the record returns 

 to the zero line of normal equilibrium. The after-effect of 

 pre-maximum stimulation is thus a short-lived continuance 

 of response followed by recovery. 



After-effect at maximum : Experiment 215. — In this the 

 photic stimulus was continued till the attainment of 

 maximum, when light was suddenly removed at b. The 

 after-effect was no longer a persistence of responsive 

 movement, but disappearance of negativity and recovery 

 to zero line of equilibrium. 



Post-tnaximum after-effect : Experiment 216. — In this 

 light was continued till there was a complete neutralisation, 

 the curve of response returning to zero line ; to all outer 

 seeming the responsive indication of the tissue is the 

 same as before excitation. But stoppage of stimulus at c 

 causes an over-shooting at a rapid^^ rate far below the zero 

 line ; and it is after a considerable period that the curve 

 returns to the zero line of equilibrium. 



The condition at post-maximum c is thus one of dynamic 

 equilibrium where two opposite activities, " A " and " D," 

 balance each other ; for had the condition of the ' neutra- 

 lised ' tissue been exactly the same when fresh, cessation 

 of stimulus would have kept the ^Ivanometric spot of 

 light at the zero position. 



The electric investigation described above shows that 

 the after-effect is modified by duration of stimulation, and 

 that : 



(1) the after-effect of pre-maximum stimulation is 



the continuation of response in the original 

 direction (upward, and away from zero line), 

 followed by recovery, 



(2) the after-effect of the maximum is an electric 

 recovery towards zero position, and 



