SUMMARY 99 



It has been shown that direct and indirect stimulation 

 induce two opposite reactions : direct stimulation induces 

 diminution of turgor, contraction and retardation of growth 

 {cf. Experiments 53, 54, 55, 57) ; indirect stimulation induces, 

 on the other hand, increase of turgor, expansion and 

 enhancement of the rate of growth [cf. Experiments 52, 

 56, 57). The indirect stimulation is transmitted not only 

 longitudinally, but also across the organ. 



Applying these principles to the explanation of the 

 anomalous case described by Fitting, the reason why only 

 those points on the directly stimulated under or proximal 

 side exhibit response which are opposite to corresponding 

 unstimulated areas on the upper or distal side, would appear 

 to be this : that the remaining unresponsive points on the 

 under or proximal side are opposite to corresponding 

 stimulated areas on the upper or distal side from which 

 indirect stimulation is transmitted which has an inhibitory 

 effect. 



The effects of direct and indirect stimulation and the 

 general mechanism of tropic curvature are treated of in 

 greater detail in Chapter XII. 



Summary 



The response' of a tendril is in no way different from 

 that of growing organs in general. 



Mechanical stimulus directly applied induces incipient 

 contraction, that is, retardation of the rate of growth, the 

 effect being similar to those induced by other modes of 

 stimulation. 



Stimulus of contact or of friction induces a moderate 

 retardation in the rate of growth. On the cessation of 

 stimulation, the normal rate is restored within a short 

 time. 



Under unilateral mechanical stimulation of short dura- 

 tion, the directly excited proximal side undergoes contraction, 

 the indirectly stimulated distal side exhibits the opposite 

 reaction of expansion. The induced curvature is thus 



