MULTIPLE RESPONSE 293 



Multiple response caused by strong stimulation in 

 Desmodium. — I next tried to find out whether Desmodium 

 in a state of standstill would give multiple responses to a 

 strong chemical stimulation, as I had found Biophytum to do. 

 Remembering how successive twitches are produced in a 

 frog's muscle, in a nerve muscle preparation, when the nerve 

 is touched with salt, I applied a strong solution of the same 

 reagent to the petiolule of the arrested Desmodium leaflet. 

 This gave rise to a series of four vigorous mechanical 

 pulsations. 



In order again to show that multiple response could be 

 initiated by strong thermal stimulus, in Desmodium as in 

 Biophytum, I selected a plant whose leaflets were in a state 

 of natural standstill. A fairly strong stimulus was applied 

 by means of the thermal stimulator, at a point on the petiole 

 half a centimetre above the insertion of the motile leaflet, in 

 precisely the same manner as was ordinarily done with 

 Biophytum. The Desmodium leaflet now gave a multiple 

 series of responses, exactly similar to those obtained from 

 Biophytum. The first occurred three and a half minutes after 

 the application of stimulus. The successive rise and fall were 

 then uninterrupted. The average period of each response in 

 the series was approximately 4/5 minutes. The multiple 

 responses gradually declined in amplitude, and came to a 

 stop after the thirteenth oscillation. It is thus seen that 

 a strong stimulus will give rise to a multiple series of re- 

 sponses in the case of Desmodium, precisely as in that of 

 Biophytum. 



It is now clear that there is no rigid line of demarcation 

 between multiple and automatic responses. An ordinarily 

 responding plant like Biophytum, which gives a single response 

 to single moderate stimulus, and multiple response to strong 

 stimulus, will, under very favourable circumstances, that is to 

 say, when it has absorbed an excess of energy from without, 

 become automatically responding ; and, conversely, the pro- 

 nouncedly automatic Desmodium will, under unfavourable 

 circumstances, that is to say, when the sum total of its latent 



