356 RESEARCHES ON IRRITABILITY OF PLANTS 



of increasing intensity, the amplitudes of the successive 

 responses remain the same. The response is, therefore, on 

 ' all-or-none principle.' After the stimulus intensity has 

 reached a certain limit the excess of absorbed energy finds 

 expression in multiple responses. Certain plant tissues 

 have thus the power of holding the excess of stimulus latent, 

 to be given out later in the form of recurrent responses 

 (p. 282). 



The characteristics of the response of Biophytum are 

 like those of cardiac tissue of the animal. Both are charac- 

 terised by a long refractory period and response on ' all-or- 

 none principle.' In both a single moderate stimulus gives 

 rise to a single response and strong stimulus to a multiple 

 series of responses. 



There is no strict line of demarcation between the 

 phenomenon of multiple and of spontaneous response so 

 called. Under very favourable circumstances of absorption 

 of excess of energy from without an ordinary responding 

 plant like Biophytum will become converted to an auto- 

 matically responding plant like Desmodium gyrans. 



Automatic Pulsations of Desmodium gyrans 



No satisfactory theory has been offered in explanation 

 of the so-called spontaneous movement. It has, however, 

 been shown in this and in my previous work that there 

 is no such thing as an absolutely spontaneous movement, 

 but that every movement is the result of the action of 

 stimulus which has been stored up. That this is the case 

 may be demonstrated in the case of Desmodium by isolating 

 the leaflet from external sources of stimulation. The effect 

 of run down of stored up energy is then seen in the gradual 

 stoppage of the pulsatory movement. In this condition of 

 standstill response occurs under fresh stimulation. If the 

 depletion of energy has not been excessive, then a moderate 

 stimulus gives rise to a multiple series of responses. But, 



