PULSATIONS OF DESMODIUM GYRANS 291 



unlike the rhythmic movement of the heart. The extra- 

 ordinary similarity under various conditions of the rhythmic 

 reactions in the plant and the animal will be seen in the 

 experiments which will be presently described. 



It will, moreover, be shown that, strictly speaking, there 

 is no such thing as spontaneous movement. The energy 

 which expresses itself in pulsating activity is derived by the 

 plant either directly from immediate external sources or 

 from the excess of such energy already accumulated and 

 held latent in the tissue. When the storage is exhausted, 

 the spontaneous movement, so called, is found to cease. 

 In this condition of standstill the rhythmic activity can be 

 renewed by an accession of fresh stimulus. 



In the intact plant, under favourable conditions, these 

 spontaneous movements are observed to take place more or 

 less continuously ; but there are times when they come to a 

 standstill. For this reason and because of the fact that a 

 large plant cannot easily be manipulated as a whole and 

 subjected to the various changing conditions which the 

 purposes of investigation demand, it is desirable if possible 

 to experiment with the detached petiole carrying the pul- 

 sating leaflet. The required amputation, however, may be 

 followed by arrest of the pulsating movements. But, as in 

 the case of the isolated heart in a state of standstill, I find 

 that the movement of the leaflet can be renewed in the 

 detached specimen by the application of internal hydrostatic 

 pressure. Under these conditions, the rhythmic pulsations 

 are easily maintained uniform for many hours. This is a 

 great advantage, inasmuch as in the undetached specimens 

 the pulsations are not usually found to be so regular as they 

 now become. So small a specimen, again, can easily be 

 subjected to changing experimental conditions, such as 

 variations of internal hydrostatic pressure and temperature, 

 application of different drugs, vapours, and gases. 



The petiole after detachment should be put in water 

 immediately, to prevent complications arising from drying 

 of the cut end. It is then mounted water-tight, in the 



