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LIFE MOVEMENTS IN PLANTR 



of the tendril of Passiflora did not induce any response, 

 yet it inhibited the normal response of the under side. 



The results of experiments which I have described will, 

 however, afford a satisfactory ex- 

 planation of this curious inhibition. 

 It has been explained, that the 

 curvature of the tendril is due to 

 the joint effects of diminished 

 turgor and contraction at the 

 directly stimulated side, and an 

 enhancement of turgor and ex- 

 pansion on the opposite side. In 

 the diagram seen in figare 106, 

 the left is the more excitable side, 

 and contraction will induce con- 

 cavity of the stimulated side. But 

 if the opposite or less excitable side 

 of the tendril be stimulated at the 

 same time, then the transmitted 

 effect of indirect stimulus will 

 induce enhancement of turgor and 

 expansion on the left side, and 

 thus neutralise the previous effect 

 of direct stimulus. An inhibition 

 of response will thus result from 

 the stimulation of the . opposite 

 side. 



A difficulty arises here from the fact that the upper 

 side of the tendril (the right side in Fig. 106) is supposed 

 to be inexcitable and non-contractile. Hence there may be 

 a misgiving that the stimulation of the non-motile side 

 may not induce the effect of indirect stimulus (an 

 increase of turgor and expansion) at the opposite side, 

 which is to inhibit the response. But I have shown that 

 even a non-contractile organ under stimulus generates both 



Fig. lot). — Diagrammatic re- 

 presentation of effects of In- 

 dii-ect and Direct unilateral 

 stimulation of the tendril. 

 Indirect stimulation, I, induces 

 movement away from stimulated 

 side (negative curvature) repre- 

 sented by continuous arrow. 

 Direct stimulation, D, induces 

 movement towards stimulus 

 (positive curvature) indicated 

 by dotted arrow. 



