MULTIPLE RESPONSE 28 I 



of excitations. I was therefore led to expect that this 

 fact might be demonstrated in another and still more con- 

 vincing manner, if I should succeed in finding a sensitive 

 plant which exhibited these multiple excitatory waves by 

 repeated movements of the indicating motile leaflets. 



Certain peculiarities of BiopJiytuiii which I had previously 

 discovered led me to think that I might find in this plant the 

 opportunity I sought ; for we have seen in the last chapter 

 that in Biophytuiu a certain minimal intensity of stimulus 

 induced the maximal mechanical response. With such 

 a stimulus we obtain only one response, and if we apply 

 a stimulus of very much more than minimal intensity it 

 produces no greater mechanical effect. What, then, happens 

 to the excess of stimulus ? This excess may be wasted as 

 heat, or it may continue to exist in some latent form, 

 and this latent stimulus may subsequently be given out 

 rhythmically. 



Multiple mechanical responses. — In view of these facts 

 I expected a strong stimulus to give rise to those periodic 

 waves whose existence I had been led to suspect from the 

 observation of the recurrent electromotive and electrotactile 

 waves in various plants. As a matter of fact it has been 

 noticed that Biophytmn, when strongly excited, exhibits two 

 successive movements of mechanical response, the leaflets not 

 completing their closure at once, but in the course of two 

 twitches succeeding each other. But I expected to detect 

 a larger number of pulsatory movements in response to a 

 single strong stimulus. 



In order to do this, however, it was necessary to prevent 

 the complete closure of the leaflets, by which the further 

 exhibition of mechanical response was made impossible. 

 For this purpose I used the Optic Lever, with the light 

 counterpoise (p. 19). In this way I succeeded in demon- 

 strating, through mechanical response, what had already 

 been demonstrated electrically, the fact that a single strong 

 stimulus, of whatever form — thermal, mechanical, electrical, 

 or photic — will induce, not one but a multiple series of 



