EFFECT OF DEPLETION OF ENERGY 311 



I stated in a previous chapter that, strictly speaking, 

 there is no such thing as spontaneous movement ; that 

 the energy which expresses itself in the pulsating activity of 

 the plant is in reality derived from external sources. It is 

 thus the stimulus supplied by the environment which is 

 held latent by the plant-tissue to find expression later in 

 rhythmic pulsations. For the experimental demonstration of 

 this theory we may carry out the following investigations : 



(i) The effect of stimulus on the pulsating activity of a 

 specimen in a moderately sub-tonic condition. 



(2) The effect of stimulus on a leaflet in a state of stand- 

 still. The renewal of pulsation by absorption of energy has 

 already been shown in the records given in figs. 150, 151, 152, 

 and 153. 



(3) Observation of the effect of gradual depletion of 

 energy on the pulsation of the leaflets. 



(4) Effect of fresh stimulation on specimens in which 

 the stored energy has been allowed to run down. 



Effect of Stimulus on Sub-tonic Specimens 



We take a specimen in which the pulsating activity is 

 moderate or feeble, and subject it to stimulation. If the 

 rhythmic activity is the result or after-effect of stimulus 

 previously absorbed, then a more vigorous pulsation may 

 be expected from the greater accession of energy. 



This inference is found fully verified in the record given 

 in fig. 155. The specimen had been kept in the dark, and 

 its pulsating activity was only moderate as seen in the first 

 part of the record. The leaflet was then subjected to the 

 stimulus of light from a Nernst electric lamp for half an 

 hour. The record taken after this interval shows a marked 

 enhancement in the amplitude of pulsation. 



Effect of Gradual Depletion of Energy 



Having observed the effect of accession of energy, it is 

 still more interesting to note the effect of the converse process 

 of gradual depletion of energy. I had hitherto been relying on 



