454 COMPARATIVE ELECTRO-PHYSIOLOGY 



be reversed, flowing now from B->A". A point of transition, 

 or of balance, A', may now be found by searching, at which 

 the movement of the exploring contact, nearer or further, 

 will give rise to opposite responsive currents. The con- 

 ductivity along the longitudinal direction will then be, to 

 that in the transverse direction, as the balancing- distance 

 CA' is to CB. With a given specimen of the peduncle 

 of Musa the transverse distance CB was 37 cm., and the 

 longitudinal balancing-distance CA" was determined at 10-4 

 cm. Hence the longitudinal velocity was 2'8 times that in 

 the transverse direction. 



FIG. 273. Experimental Arrangement for Comparing the Relative 

 Conductivities in Transverse and Longitudinal Directions 



C, point of application of stimulus ; B, permanent transverse contact ; 

 A, A', A", exploring points of longitudinal contact for obtaining 

 balance. 



It has been shown that different tissues in the plant may 

 possess extremely different powers of conducting stimulus. 

 In animals there are specialised channels of conduction 

 known as nerves, and in plants also I have been able to 

 discover similar conducting tissues, which can be isolated 

 for the study of their responsive peculiarities. Experiments 

 on this subject will be related in detail in Chapter XXXII. 

 It may be said here, however, in anticipation, that the 

 velocity of transmission of true excitation through these 

 nervous channels is, generally speaking, fairly high, being at 

 the rate of about 50 mm. per second in the case of isolated 



