TRANSMISSION OF EXCITATORY WAVES IN PLANTS 247 



by using thermal stimulation. It was thus found that the 

 excitation caused by a strong, would travel with a greater 

 velocity than that due to feeble stimulus, the one being 

 sometimes double the other. I next tried to obtain quan- 

 titative results, by using a form of stimulus which was 

 measurable, and could be increased in a graduated manner. 

 For this I employed the method of stimulation by condenser 

 discharge, the stimulus being increased by increasing the 

 E.M.F. that charged the condenser ( - oi microfarad). 



In one series, with a stimulus of eight-volt charge, the 

 velocity found was 18 mm. per second. When the stimulus was 

 increased by charging the condenser to twelve volts, there was 

 an increase of velocity to 1*9 mm. per second. And finally, 

 with a sixteen- volt charge, the velocity was found to be 2*1 mrn. 

 per second. These velocities referred to centripetal trans- 

 mission. In the next series, the experiments were carried 

 out on a much more excitable leaf, and the velocity was 

 determined in a centrifugal direction ; with a charge of eight 

 volts, the velocity was 3*27 mm. per second ; with sixteen volts, 

 it rose to 376 mm. ; and with thirty-two volts, it became 

 3*83 mm. per second. The two following tables exhibit these 

 results of increasing velocity with increasing stimulus : 



Tables showing Increase of Velocity with Increasing Stimulus 



Specimen I. — Centripetal transmission. 



The distance traversed by stimulus was 27 mm. 



Specimen II. — Centrifugal transmission. 

 Distance traversed by stimulus was 38 mm. 



Stimulus 



Time 



•01 microfarad charged to 8 volts 

 24 ,, 



1 1 - 6 seconds 

 IO'2 ,, 

 io-i ,', 

 9'9 >> 



Velocity 



3-27 mm. per second 

 3-72 mm. ,, 



3-76 mm. ,, 



3-83 mm. ,, 



