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 T employed the method of stimulation by condenser 

 discharge, the stimulus being increased by increasing the 

 E.M.F. that charged the condenser (01 microfarad). 



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

 velocity found was r8 mm. per second. When the stimulus was 

 increased by charging the condenser to twelve volts, there was 

 an increase of velocity to r9 mm. per second. And finally, 

 with a sixteen-volt charge, the velocity was found to be 2t mm. 

 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 showinc; Incre.a.se ok Velocity with Increasing Stimulus 



Sped men I. — Centripetal transmission. 

 The distance traversed hy stimulus was 27 mm. 



