146 RESEARCHES ON IRRITABILITY OF PLANTS 



was at a distance of 30 mm. from the pulvinus, and the 

 frequency of the vibrating-recorder employed was 10 times 

 in a second. 



In the lowest of the three records shown in fig. 86 a 

 stimulus-intensity of "5 was employed. The next record, 

 the highest in the figure, was taken with stimulus 2, that 

 is to say, four times the former intensity, and the time of 

 transmission was found to be practically the same as with 

 the feeble stimulus. The third, which is the intervening 

 record, was taken when the stimulus had been restored to 

 its original feeble intensity of -5. The results demonstrate 

 that these successive experiments, with varying intensities 

 of stimulus, gave practically uniform results in velocity of 

 transmission of 20 mm. per second. 



These experiments confirm the conclusion that when 

 the plant is in an optimum condition its velocity of trans- 

 mission is practically constant, even under varying intensity 

 of stimulus. In ordinary circumstances the velocity in- 

 creases with increasing intensity of stimulus, till a limit is 

 reached under maximal stimulation. 



Disturbing Action of Leakage of Current 



On employing the very strong stimulus-intensity of 15 

 or 20 units, I have sometimes observed a sudden enhance- 

 ment of the normal velocity. In fact, the time elapsing 

 in these circumstances between stimulus and response was 

 tantamount to the duration of the latent period, the velocity 

 of transmission being thus practically infinite. One thing 

 that was noticeable in such experiments was that instead 

 of gradual and continuous enhancement of the velocity, 

 with increasing stimulus, the enhancement which occurred 

 was sudden and abrupt at a certain high intensity. This 

 justifies the conclusion that, in such a case, the stimulation 

 becomes virtually direct by leakage of currents of relatively 

 high tension. 



