MULTIPLE RESPONSE 289 



In connection with this, I have observed, among the 

 types of cyclic variation in multiple response in plants, an 

 instance in which every third response was missing, the period 

 of each second beat being thus approximately twice as long 

 as that of the first. It was easy to see that this was an 

 instance of alternating fatigue, causing the particular record- 



FlG. 122. Intermiltence in Pulsation of /«Vr;//?j'///w 



ing leaflet to just miss the response every third time (p. 122). 

 That the excitatory wave arrived in regular sequence, was 

 seen by the fact that the neighbouring leaflets pulsated at 

 regular intervals. 



Semi-automatism. — The plant Biophytuin growing in 

 the open, under favourable conditions of heat. and light, some- 

 times becomes so excessively sensitive that motile impulses 

 are generated, the stimulus causing which it is often difficult 

 to localise. A particular leaflet may have been moved by a 

 puff" of wind ; or the alighting of a small insect, or the accidental 

 grazing of an adjacent blade of grass, may have been the 

 original source of the impulse. But this is enough to set all 

 the leaflets of the plant quivering in an extraordinarily lively 

 manner. For from the excited leaflet, the impulse travels 

 inwards, the leaflets falling in centripetal succession. The 

 excitatory wave then reaches the stem and overflows to the 

 other leaves. But this time the progressive closure of the 

 leaflets proceeds in a centrifugal or outward direction. 

 Before the first discharge, however, going through the 

 numerous avenues, can exhaust itself, the second impulse of 

 the multiple response may begin ; and in this way the leaf- 

 lets exhibit most lively movements without any immediate 



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