346 PLANT RESPONSE 



(2) In possession of long refractory period. — In order to study- 

 in detail the characteristics of response in Desmodium, I took 

 a plant in which the leaflets had come to a state of natural 

 standstill. To such a specimen I applied the stimulus of a 

 condenser discharge ; it was found, as stated already, that 

 a rather high electromotive charge (twenty-four volts) was 

 required to produce response. The first few responses were 

 somewhat feeble, owing to the sluggish condition of the tissue ; 

 they then increased in a ' staircase ' manner till they became 

 uniform, the period of a complete response being now about 

 six minutes. From this point on, the responses were the 

 maximal possible, and a higher E.M.F. produced no notice- 

 able increase. The most characteristic feature of these 

 responses was the possession of a long refractory period, 

 which we have also found to be characteristic of the response 

 of Biophytum. With this specimen of Desmodium I found 

 that when a second stimulus was given after three minutes, 

 there was no further response. But a stimulus given after 

 three and a half minutes was effective. It may be mentioned 

 here that the length of the refractory period varies somewhat 

 with the condition of the tissue, being relatively longer when 

 that is sluggish. 



(3) In incapability of tetanus. — The rhythmic tissue of 

 Desmodium thus resembles cardiac tissue, in the possession 



Fig. 145. Record showing that Rhythmic Tissue of Desmodium is 

 Incapable of being Tetanised 



After the first two pulsations, strong tetanising electric shocks were applied 

 continuously. No tetanic effect was produced, but the pulsation 

 became somewhat irregular. 



of a marked refractory period. There is again another 

 interesting similarity. A rhythmically beating cardiac tissue 

 cannot be thrown into tetanus by quickly recurring electric 



