294 LIFE MOVEMENTS IN PLANTS 



The immeJiate and after-effects of mschauical stimulus 

 on the tendril are therefore the same as that of electric 

 stimulus. The incipient contraction under direct mechani- 

 cal stimulus, moreover, is not the special characteristic of 

 ten<lrils, but of growing plants in general. For I hav,^ 

 shown (page 203) that the growth of flower stalk of 

 Zephyranthes is also retarded afier me3hanical friction, 

 from the normal rate 0*48 fM to 0*1 1. fi after stimulation. We 

 shall find later that different plant organs, after moderate 

 stimulation, exhibit acceleration of growth as an after- 

 effect. The phenomenon of responsive reaction of tendril 

 is therefore not unique, but similar to that of other organs 

 under all forms of stimulation. The only speciality in 

 tendril is that owing to anatomical p3culiarities, the percep- 

 tive power of the organ for mechanical stimulus is highly 

 developed. 



We are now in a position to offer an explanation of 

 the induced concavity of the stimulated side of the tendril, 

 and its recovery after brief contact. The experiments that 

 have been described show that : 



(1) the proximal side contracts because it is directly 



stimulated, and the distal side, being indirectly 

 stimulated, expands ; the curvature is thus due to 

 the joint effects of contraction of one side, and 

 expansion of the opposite side, and 



(2) the recovery of the tendril after brief contact is 



hastened by the after-effect of stimulus, which 

 is expansion and acceleration of growth. 



The results given above will also be found to explain 

 Fitting's important observations* that (a) the stimulated 

 side of the tendril undergoes transient contraction with 

 subsequent asceleration of growth, and that (/>) the distal 

 or co.wex si 1 ■ unln-go.^s an immeliata enhancement of 

 growth. 



* PfeHet— Ibid— \ol 111, p. 57. 



