TRANSMISSION OF IMPULSE 



123 



Experiment 72. Transmission under radio-thermal 

 stimulation. — Application of radio-thermal stimulus gave 

 rise to results essentially similar. The intensity of stimula- 

 tion was relatively stronger, and the negative excitatory 

 impulse reached the distal side (after the hydraulic positive) 

 in the course of 25 seconds (fig. 67), the velocity of the 

 impulse being o -08 mm. per second. 



Fig. 66. 



Fig. 67. 



Fig. 66. 



Effect of transverse transmission of impulse under 

 electric stimulation E. 



Fig. 67. Effect of transverse transinission of impulse under 



radio-thermal stimulation T. 



Note parallel effect exhibited in figs. 65, 66, 67 ; also slow fall of 

 leaf in the commencement becoming suddenly rapid, as 

 shown by the scratch line. (Mimosa.) 



The experiments that have been described are of much 

 significance. A rigid organ like the stem of Mimosa may 

 appear insensitive to stimulation, since it exhibits no 

 responsive movement ; but its perception of stimulus is 

 shown by its power of initiation and transmission of two 

 characteristic impulses to a distance, one of which is the 

 positive giving rise to an enhancement of turgor at the 

 distal side, and the other the true excitatory negative 

 inducing the opposite effect of diminution of turgor. Uni- 

 lateral stimulation gives rise to both these effects in all 

 organs — pulvinated, growing and non-growing. It is the 



