382 COMPARATIVE ELECTRO-PHYSIOLOOy 



multiple movement of its leaflets is arrested. If the plant, 

 for instance, be kept for some time in a dark room, the leaf- 

 lets cease to pulsate. But if now an electrical shock of 

 moderate intensity be given to the pulvinus, the incident 

 stimulus, by its excitatory action, gives rise to a number of 

 responsive movements, which again come to a stop as soon 

 as the imparted energy is exhausted. Or we may, in such a 

 case, employ the stimulus of light. A record of the subse- 

 quent effect has already been given on a previous page 

 (cf. fig. 141). 



It will there be noticed (i) that the quiescent leaflet is 

 thrown into pulsatory movements after the lapse of a short 

 latent period ; (2) that the increasing absorption of stimulus 

 has the effect of augmenting the amplitude of response ; and 

 lastly (3) that, owing to the presence of latent energy derived 

 from the impinging stimulus, the activity of the leaflet con- 

 tinues for some time, even on the cessation of stimulus itself. 

 It is, in fact, by that enhancement of the tonic condition, 

 which comes about by the continuous absorption of energy 

 from the environment, that the apparently autonomous 

 response of the leaflet is maintained. There is, as has been 

 said before, no essential difference between multiple and 

 autonomous response. A tissue, which was responding 

 autonomously, comes to a state of standstill when its store 

 of latent energy falls below par. Conversely, by the acces- 

 sion of energy from external stimulus, activity is resumed, 

 multiple passing into autonomous response. 



Returning, then, to the hydraulic mode of response, as 

 observed in variations of suction, we might expect that the 

 impact of stimulus would initiate this in a tissue at suctional 

 standstill. For this experiment I took a specimen of Croton 

 and mounted it, with terminal electrodes, in the Shoshun- 

 graph. At this time it showed a moderate rate of suction. 

 It was then kept undisturbed in a dark room for forty-eight 

 hours, at the end of which time, owing to the run-down of its 

 latent energy, the suctional activity was found to be arrested. 

 But on the application of electrical stimulation, the suctional 



