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



7. General Considerations. 



The contradictory nature of the various responses is, however, not real ; 

 the apparent anomaly lies in the fact that two distinct fundamental reactions 

 to stimulus had hitherto remained undiscovered. The innumerable variations 

 in the resultant response is due to the summation of the effects of two 

 fluctuating factors ; it is therefore most important to have the means of 

 tracing the continuous change in the response brought about by the two 

 elements which are sometimes in accord and at other times in conflict. The 

 autograph of the plant itself giving a history of the change in response and 

 its time-relations is therefore decisive in explanation of the various 

 anomalies in plant-movements, as against the various tentative theories that 

 have been put forward. The analysis of the resultant effect thus rendered 

 possible casts new light on responsive characteristics of various organs, such 

 as the localisation of the sensory zone in Avena, the illusive difference 

 between tropic and nastic movement, and many other anomalies which are 

 more apparent than real. Limitation of space compels me to confine myself 

 to the consideration of some important and typical reactions which will give 

 clue for the explanation of others. 



All the tropic movements under unilateral stimulus find their explanation 

 from the above laws of direct and indirect stimulation that have been 

 established for all modes of excitation. We have henceforth to deal with 

 two classes of effects, due to longitudinal and transverse transmission 

 respectively. In the former case the transmitted stimulus will cause an 

 expansion higher up on the same side to which the stimulus is applied ; the 

 result will be an induced convexity, a movement away from stimulus, i.e., a 

 negative curvature. In the case of transverse transmission, the direct effect 

 on the proximal side will be a contraction, and on the opposite side an 

 expansion. When the stimulus is feeble, or when the tissue is a non- 

 conductor of excitation, the first positive will remain as the final effect. But 

 in other cases, conduction of excitation in a transverse direction will bring 

 about a neutralisation or even a reversal into negative. These theoretical 

 deductions I have put to the test of experiment. 



8. Tropic Curvature with Longitudinal Transmission of Stimulus. 

 Expt. 7. — I have already explained how thermal radiation is almost as 

 effective in inducing contraction and retardation of growth as the more 

 refrangible rays of the spectrum. The thermal radiation is produced by the 

 heating of a platinum spiral, short of incandescence, by the passage of an 

 electric current. The intensity of radiation is easily varied by adjustment of 



