RENEWAL OF PULSATION 307 



quiescent leaflet was then subjected to the continued action 

 of light from a Nernst lamp. It will be noted that by the 

 absorption of the energy of light the leaflet regained its 

 so-called spontaneous activity. 



It should be mentioned here that the effect induced by 

 the stimulus is, to a certain extent, modified by the tonic 

 condition of the plant. In a sub-tonic specimen, with the 

 leaflet in a state of standstill, the action of stimulus is to 

 renew the pulsating activity. In a different specimen, 



Fig. 150. — Action of light in renewing the pulsation of Des- 

 modium leaflet at standstill. Light was applied at the point 

 indicated by the arrow and continued afterwards. 



where the rhythmic activity is feeble, the incidence of 

 stimulus enhances the amplitude of pulsation. If the 

 leaflet should be in a vigorous condition, excessive stimu- 

 lation is apt to bring on fatigue, in consequence of which 

 the pulsations become either irregular or diminished in 

 amplitude. These various effects are found to take place 

 not only under the action of stimulus of light but, as we 

 shall see, under electric stimulus also. 



Effect of Electric Stimulus 



The leaflet of Desmodium in a state of standstill may 

 have its activity revived by other modes of stimulation, 



