396 



Sir J. G. Bose and Mr. G, Das. 



4. These effects are accentuated by the differential excitabilities of the two 

 halves of an anisotropic organ. 



D. Eelation between Eesponse to Stimulation of Geowing and of 



Non-growing Organs. 



18. Similarity of Response of Growing and of Non-growing Organs. 



I have throughout this paper adduced numerous instances of the essential 

 similarity between the response of motile and that of growing organs. The 

 following tabular statement will show that a fundamental reaction finds 

 expression in diverse ways, according to different methods of recording 

 response in motile, non-motile, and growing organs : — 



Table IV. — Mechanical and Electrical Eesponses in Motile, Non-motile 



and Growing Organs. 



Inducing cause. 



Change of form. 



Mechanical response. 



Electrical response. 



Direct stimulation 

 Indirect stimulation 

 Effect of increasing turgor 



Contraction 



Expansion 



Expansion 



Fall of leaf ; 

 negative response 



Erection of leaf ; 

 positive response 



Erection of leaf ; 

 positive response 



Negative response. 

 Positive rosponse. 

 Positive response. 



It has been shown that any agent which increases the excitability of 

 pulvinated organs, as measured by the amplitude of response, mechanical or 

 electrical, likewise induces a positive variation or enhancement of the rate of 

 growth. Conversely, a depressor which brings about a diminution in the 

 amplitude of their mechanical and electrical response also causes depression 

 in the normal rate of growth. 



The tropic effect of light is the same on growing as on motile organs. 

 The particular rays which are effective in one case are also effective in the 

 other. Eed and yellow rays are ineffective in both. In one case, as in others, 

 we obtain the positive, the dia-positive, and the negative. The tropic move- 

 ments are determined in both by the same combination of the effects of 

 direct and indirect stimulation. 



Owing to the varying combinations of effects of numerous unknown factors 

 the phenomenon of growth presents many perplexities. We may take, for 

 example, the case of the action of external stimulus on growth. Here sub- 

 minimal stimulus induces one effect and moderate stimulus the very opposite. 



