314 RESEARCHES ON IRRITABILITY OF PLANTS 



stored energy is well seen in the regular diminution of the 

 amplitude and the prolongation of the period ; there are 

 now, in the lower or earlier series, twenty-three pulsations 

 in the course of eighty minutes, instead of twenty-seven, 

 which was found at the beginning. The period becomes 

 still more prolonged in the next series, where there are only 

 twenty pulsations. The pulsating activity of this specimen 

 was found completely arrested at the end of the ninth hour. 

 In another specimen less vigorous, the arrest took place 

 at the seventh hour. I give a record taken during the 

 seventh hour (fig. 157) which shows the process of arrest 

 in a very interesting manner. 



Renewal of Pulsation under Fresh Stimulus 



The arrest of pulsation seen here is not due to death 

 or loss of sensibility, but merely to the run down of stored 

 energy. I shall presently show that the activity of the 

 leaflets can in these cases be renewed by the incidence of an 

 external stimulus. Before describing the experiments, it is 

 well to anticipate the modifying results brought on by the 

 varying loss of stored energy. The extent of depletion will, 

 it is obvious, depend on the length of time during which 

 the specimen had been kept isolated from the external 

 supply. At the moment of arrest of pulsation the specimen 

 will still have a certain reserve, but not enough to cause an 

 overflow. At this stage a stimulus of even short duration 

 is likely to give rise to multiple responses. If we allow a 

 longer time to elapse after the stoppage of pulsation, then 

 the storage-level will be much lowered. A more intense 

 stimulus or one of longer duration will now be effective ; the 

 response is more hkely to be single rather than multiple. 

 And lastly, if we allow a very long time to elapse after the 

 cessation of pulsation, the vitality will be found to have 

 so far declined as to bring about the condition of death. 

 To recapitulate : the effect of fresh incidence of stimulus on 

 a leaflet brought to a state of standstill by isolation will 

 be modified according to the period which had been allowed 



