312 RESEARCHES ON IRRITABILITY OF PLANTS 



chance specimens for exhibition of the condition of standstill. 

 As the previous history of the particular specimen was not 

 known from moment to moment, no definite information was 

 available as to the cause of the stoppage of pulsation, except 

 the very natural inference that it must have been due to 

 the run-down of the stored energy. In order to verify this 

 inference, I now proceeded deliberately to isolate an active 

 specimen from all accession of energy from outside, and 

 observe the effect of gradual depletion of energy that had 

 been stored up. The cut specimen, mounted in the usual 



Fig. 155. — After-effect of stimulation on pulsation of Desmodium 

 leaflet in sub-tonic condition. 



manner, was kept in a dark room, and a continuous record 

 of its pulsations was taken all the time. 



In taking a series of such records under isolation, it was 

 found that the persistence of the rhythmic activity depended 

 on the vigour of the specimen — that is to say, on the storage 

 of energy in the tissue. Thus a vigorous specimen exhibited 

 persistent activity for more than twenty hours ; its pulsations 

 showed great uniformity for the first twelve hours, after 

 which the amplitude began to decline and the rhythmic 

 beat came to a stop at the twenty-first hour. 



In another specimen, less vigorous, the pulsations of the 

 isolated specimen came to an end at the ninth hour. A 



