184 RESEARCHES ON IRRITABILITY OF PLANTS 



on different specimens of Biophytum. In some cases the 

 stimulus applied was on the stem, the distance mentioned 

 being the sum of the length of stem and petiole through 

 which the two impulses were transmitted. 



It has thus been shown that under the action of various 

 modes of stimulation two distinct impulses are transmitted, 

 of which the positive travels faster than the negative. The 

 specimen employed for these demonstrations was Biophytum 

 sensitivum. I next proceed to show that these results 

 are not confined to any particular plant but are universally 

 present. 



Exhibition of Positive and Negative Impulses by 

 Different Plants 



Averrhoa carambola. — The velocity of transmission of 

 excitation in the petiole of this plant is low, being i mm. per 

 second or even less. In the first experiment of the series 



1 applied the stimulus 

 of induction-shock at 

 the moderate distance 

 of 10 mm. from the 

 responding leaflet, and 

 obtained automatic re- 

 cord by means of the 

 Oscillating Recorder. 

 The successive dots here 

 are at intervals of 



2 seconds. It will be 

 noticed that a respon- 

 sive movement of erection took place after an interval of 

 three dots or 6 seconds ; the negative response occurred 

 after the much longer interval of 20 seconds (fig. 98). 



In the next experiment with a different specimen stimulus 

 was applied at a distance twice as great as in the previous 

 case, that is to say, 20 mm. The positive response took 



Figs. 98, 99. — Positive followed by nega- 

 tive response in Averrhoa carambola 

 due to indirect stimulation. 



