TRANSMISSION OF EXCITATORY WAVES IN PLANTS 245 



fresh, to traverse this distance was 14*3 seconds. In the next 

 experiment, when the stimulus was applied after three minutes, 

 there was a slight residual fatigue, and this prolonged the 

 time to 14*5 seconds. On the third occasion, a still shorter 

 time, namely two minutes, was allowed for rest, and the rate 

 of transmission became slower, the time being now 157 

 seconds. The next interval of rest was still further shortened, 

 to one minute, and the time of transmission was correspond- 

 ingly increased to 16*4 seconds. And lastly, when the 

 stimulus was given after an interval of only half a minute, the 

 velocity was still further retarded, the time now taken being 

 175 seconds. 



The following table gives the different velocities under 

 increasing fatigue, and the heights of the corresponding 

 responses. It has already been said that the distance through 

 which the stimulus was transmitted was in all cases the same, 

 namely 27 mm. 



Table showing Variations of Velocity of Transmission and of 

 Amplitude of Response in Biophytum, with Increasing Fatigue 



Intervals of rest 



The plant fresh 

 3 minutes 

 2 minutes 

 1 minute 

 h minute 



Time 



14*3 seconds 

 14-5 ,* 

 157 » 

 16-4 ,, 



17-5 » 



Height 

 of response 



34 dns. 



20 ,, 



I4-5 >> 



2-5 „ 



I'O ,, 



Velocity 



1-88 mm. per second 

 1-86 „ 

 172 „- 

 1-64 „ 

 i-54 „ 



It will be seen from this table that, while the variation of 

 velocity due to the difference of conductivity between three 

 minutes' rest and an indefinitely longer period is slight, there 

 is a considerable diminution of this velocity when the resting- 

 periods are still further shortened. It will be noted, more- 

 over, that increasing fatigue is shown not only by a regular 

 decrement in the speed of transmission, but also in an inde- 

 pendent and still more striking manner by a steady diminution 

 in the heights of the responses themselves. 



The following curve (fig. 105) shows the variation of 



