CHAPTER VII 



RESPONSIVE CURVATURE OF MOLECULARLY 

 ANISOTROPIC ORGAN 



Molecular anisotropy artificially induced by one-sided cooling — Cooled side less 

 responsive — Diffuse stimulation causes concavity of the uncoolcd, that being 

 relatively the more excitable — Local fatigue diminishes excitability — Diffuse 

 stimulation now causes concavity of the unstrained side — Similar anisotropy 

 induced in plagiotropic organs, by unilateral action of light — The lower or 

 shaded side of such organs relatively more excitable— Diffuse stimulation 

 causes current of response from lo iver to upper, and also concavity of lower 

 half — Responses of plagiotropic Cucurbita and Cw;zv^/7'///?/i' — Differences in 

 excitabilities of outer and inner surfaces of tubular organ — Complex response 

 due to successive excitations of two antagonistic halves of an anisotropic 

 organ — Response of spiral tendrils by uncurling — Response in certain cases by 

 contraction of the spiral or curling — Writhing movement in spiral tendril 

 under strong stimulation. 



We have seen that in a radial organ, owing to balanced 

 actions, there is no lateral response to diffuse stimulus ; and 

 that in dorsi-ventral organs, where there is pronounced 

 anisotropy — as seen in anatomical differentiation — lateral 

 movement is produced by means of differential action. I 

 am now about to demonstrate the fact that these phenomena 

 are not sharply divided, but merge gradually one into the 

 other, through intermediate types. 



Molecular anisotropy induced by unilateral application 

 of cold or of excessive stimulation. — If we take a hollow 

 radial petiole of Gourd {C/unrlnta niaxiind) growing erect, we 

 shall find, on application of diffuse stimulus, that it gives no 

 responsive curvature, but exhibits the simple longitudinal 

 contraction of a radial organ. We may now take this petiole, 

 and split it into two equal halves, throughout almost its 

 entire length. We have now a single specimen bifurcated, 

 the forked divisions being equal in every respect. One fork, 



