100 CHAP. X. EFFECT OF MECHANICAL STIMULATION 



due to the joint effects of the contraction of the one side, 

 and the expansion of the opposite side. 



As the after-effect of direct stimulation of moderate 

 intensity is an acceleration of growth above the normal, 

 the stimulated side undergoes an expansion by which the 

 recovery is hastened. 



Direct application of unilateral stimulus induces a 

 positive curvature, but the same stimulus applied indirectly 

 at a distance from the responding region induces a negative 

 curvature. 



The dorsiventral tendril of Passiflora is excitable on both 

 the upper and under sides ; the excitability of the under 

 side is about seven times greater than that of the upper 

 side. 



Stimulation of one side of the tendril induces expansion 

 of the opposite side, even in cases where the excitability 

 of the stimulated side is feeble. 



The response to direct stimulation of the more excitable 

 side of the tendril is thus inhibited by stimulation of the 

 opposite side, as seen in Fitting's experiment. This is a 

 case of the neutralisation of the effect of direct by that of 

 indirect stimulation. 



