252 



PLANT RESPONSE 



of dead tissue. A strong stimulus applied to the first of these 

 will now cause an excitatory expulsion of water, which will 

 be transmitted across the dead area, and impart a mechanical 

 blow to the second living tissue, thus setting up excitation 

 de novo in that portion of the petiole. 



Velocities of transmission in various plant and animal 

 tissues. — I give below a number of determinations of velo- 

 cities of transmission made with different plants, both 

 ordinary and sensitive, the electrical method of determination 

 having been used in the case of the former ; and with this, 

 for purposes of comparison, a series of values that have been 

 determined in the case of animal tissues. The respective 

 values given in the table refer to the maximum velocities 

 obtained. In this connection, it should be remembered 

 that the velocity of transmission depends on the intensity of 

 stimulus. The intensity of stimulus, again, is diminished in 

 the course of transmission through a long tract. Hence the 

 velocity near the point of application of stimulus is relatively 

 great, and becomes less the further the stimulus travels. In 

 order, therefore, to make the different results comparable, my 

 experiments have been made on equal lengths of tissue, 

 namely, 75 cm. in each case, the stimulus applied being also 

 the same. 



Tables giving Velocities of Transmission of Excitatory Wave 



{a) A in 'ma I 



Subject 



Nerve of Anodon .... 

 Nerve of Eledone (observed by Uexkiill) 



Velocity 



10 mm. per second 

 •5 to 1 mm. per second 



