TRANSMISSION OF EXCITATORY WAVES IN PLANTS 243 



menon of preferential conductivity, by which it is seen that 

 the state of excitation travels through a tissue with greater 

 facility in one direction than in the opposite. For the 

 purpose of this demonstration, I took a fresh leaf of Bio- 

 phytum. The two condenser connections (capacity "Oi micro- 

 farad charged to twelve volts) were made at A and B 

 (fig. 104). The indicating leaflet L was situated somewhere 

 between. On charge, B became the kathode, and an ex- 

 citatory wave was started in a centripetal direction. On 

 the abatement of this wave, the condenser was discharged ; 

 A now became the kathode, and an excitatory wave was 

 transmitted in a centrifugal direction. From these two 

 successive experiments, we are now able to determine the two 

 velocities in opposite directions in the same leaf. 



The following table exhibits the results obtained in this 

 manner with two different specimens : 



Excitatory discharge preferentially directed. — These 

 two observations show that the velocity is greater in the 

 centrifugal direction. In some instances I have found the 

 centrifugal velocity to be nearly twice as great as the centri- 

 petal. These experiments seem to indicate that under 

 certain conditions, excitatory discharges will take place 

 preferentially in one direction only. We may imagine any 

 intermediate point in the midrib of the leaf, to be acted on 

 locally by a gradually increasing or accumulating stimulus from 



r 2 



