ANIMAL AND VEGETABLE 137 



large motile organ at the base of the main petiole also 

 becomes bent, and again after a few seconds the stimulation 

 extends to the nearest neighbouring leaf, then to the 

 succeeding one, and so on, till at last all the leaves of the 

 shoot have made the movement/' (Sachs.) 



The rate of propagation of stimuli in the plant, as 

 compared with man, is, of course, relatively very slow. 

 That is, if we regard it as a purely physical process in the 

 sense that when a stretched string is jerked at one point 

 the whole string vibrates. But if we take the rate of 

 conduction of a feeble electrical stimulus, I do not think it 

 will be found to differ materially from the rate of conduction 

 in a human nerve. 



