CHAPTER XXIII 



EFFECT OF STIMULUS ON LEAFLET OF DESMODIUM AT 

 STANDSTILL 



Condition of standstill brought about by depletion of energy — Renewal 

 of pulsation by the stimulus of light— Response to stimulus of 

 induction-shock — Multiple response under tetanisation — Determina- 

 tion of the latent period and the apex time — Refractory period — 

 Effect of stimulus on leaflets in sub-tonic condition — Effect of isolation 

 on rhythmic activity — Gradual arrest of pulsation resulting from 

 run-down of stored energy — Effect of fresh accession of energy. 



The leaflets of Desmodium exhibit in favourable circum- 

 stances a more or less persistent rhythmic activity. But 

 this activity may cease under conditions which are less 

 favourable. The arrest may be due to either of two causes, 

 of which the first is the exhaustion of that reserve of energy 

 without which the pulsation cannot be maintained, and 

 the second is the loss of motility of the pulvinule brought 

 on by age or other factors. As a parallel instance to this 

 we have the case of Biofthytum, the old leaflets of which 

 become quite insensitive, while the plant as a whole remains 

 sensitive. 



Renewal of Pulsating Activity under the Action 

 of Stimulus 



In those cases where the arrest is due to run-down of 

 energy, the pulsation of Desmodium leaflets may often be 

 renewed by the application of appropriate stimulus. This 

 may be seen in the following record on the action of the 

 stimulus of light (fig. 150). The leaflet had been reduced 

 by extreme sub-tonicity to a state of standstill. The 



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