CHAPTER VII 



EFFECT OF ELECTRIC STIMULATION ON GROWTH 



In plant-physiology the word ' stimulus ' is often used in 

 a very indefinite manner. This is probably due to the 

 different meanings which have been attached to the term. 

 An agent is said to stimulate growth when it induces an 

 acceleration of growth. The normal effect of stimulus is, 

 as will be presently shown, the retardation of growth. It 

 is probably on account of lack of precision in the use of the 

 term that statements are often vaguely made of a stimulus 

 sometimes accelerating and at other times retarding growth. 

 In order to avoid any ambiguity, the terms stimulus and 

 stimulation are here used in a sense as definite as in animal 

 physiology. An induction electric shock, a sudden variation 

 of temperature, mechanical stimulation, for example, bring 

 about excitatory contraction in the muscle. These various 

 forms of stimulation also cause excitatory contraction of 

 the motile pulvinus of Mimosa pudica. The question 

 suggests itself whether such diverse forms of stimulation 

 evoke similar or different reactions in the growing organ. 



An opinion prevails, however, that different modes of 

 stimulation induce reactions which are specifically different. 

 The results of investigation to be given in this and in the 

 following chapters will show that this is by no means the 

 case ; for all kinds of stimulation of effective intensity 

 induce excitatory response of the nature of mechanical 

 contraction and of electromotive variation of galvanometric 

 negativity. The perception of the stimulus and the con- 

 sequent reaction ultimately arise from the excitation 



