MULTIPLE AND AUTOMATIC RESPONSE 287 



the application of a drop of hydrochloric acid on the 

 petiole. 



From these experiments it is clear that a rhythmic 

 series of effects need not have a periodic antecedent cause. 

 We see on the other hand that under strong stimulation 

 there is not only an immediate response but that the surplus 

 of energy remains over and is held latent by the tissue to 

 be given out later in the form of recurrent responses. 



It is the excess of latent or Internal Energy that gives 

 rise to phenomenon of multiple response. Sometimes we 

 may not have noticed the antecedent external stimuli the 



Fig. 139. — Multiple response induced by strong chemical 

 stimulation, 



absorption of which had contributed to that storage of 

 internal energy which gave rise to the rhythmic activity. 

 In these circumstances the pulsations appear to us as 

 spontaneous or automatic. 



Under natural conditions, the plant is exposed to the 

 action of various stimuli supplied by its environment. It 

 is exposed to warmth, to the action of light, to internal 

 hydrostatic pressure, to the action of various chemical 

 agents — present in it or absorbed by it. We have seen 

 that each of these factors exerts its stimulating action 

 independently. From the joint action of these external 

 sources of stimulation, the energy stored up by the plant 

 may become sufficiently great to cause an excitatory 

 overflow. It will thus be seen how, by the cumulative 

 effects of these various stimuli, the excitability of the 



