XXV.— TROPIC CURVATURE WITH TRANSVERSE 

 TRANSMISSION OB^ EFFECT OF STIMULUS 



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Sir .]. ('. BosE, 



Assisted hi/ 



GURUPRASANNA DaS. 



We have next to consider a very large class of pheno- 

 mena arising out of the direct stimnhition of one side and 

 its transversely transmitted effect on the opposite -side. 

 The unilateral stimuli to which the plant is naturally ex- 

 posed are those of contact, of light, of thermal radiation, 

 and of gravity. There is besides the stimulation by elec- 

 tric current. I shall presently show that these tropic 

 curvatures are determined by the definite effects of direct 

 and indirect stimulations. 



Under unilateral stimulus, the proximal side is found 

 to become concave and the distal side convex ; the organ 

 thus moves towards stimulus, exhibiting a positive curva- 

 ture. This movement may be due : (1) to the diminution 

 of turgor, contraction or retardation of rate of growth of 

 the proximal side, (2) to the increase of turgor, expansion 

 or acceleration of rate of growth on the distal side, 

 or {?)) to the joint effects of contraction of the proximal 

 and expansion of the distal side. 



As regards the reaction of the i)roximal side, it has 

 been shown that direct stimulation induces local contrac- 

 tion in a pulvinated organ, and retardation of growth in 

 a growing organ. The effect induced on the distal side 



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