184 LIFE AND WORK OF SIR JAGADIS C. BOSE 



stimulus checks growth or brings about an ' incipient ' 

 contraction ; when the intensity of stimulus is increased, 

 the effect culminates in an actual contraction. This is 

 exactly parallel to the contraction in the pulvinus under 

 direct stimulus. 



He next demonstrates the effect of Indirect Stimulus 

 (applied at some distance from the responsive region of 

 growth). This produces an expansion and acceleration of 

 the rate of growth. The opposite effects of Direct and 

 Indirect Stimulus are diagrammatically shown in Fig. 22 

 (a and b). He thus establishes his Law of Effects of Direct 

 and Indirect Stimulus : 



Direct Stimulus induces contraction ; Indirect Stimulus 

 causes the opposite effect of expansion. 



The same law applies when stimulus acts on one side 

 of the organ. When stimulus of any kind acts on the 

 right side (Fig. 22, c), the directly stimulated right side 

 contracts and the indirectly stimulated opposite, or left 

 side expands, with the result of tropic curvature towards 

 the stimulus. And from these fundamental reactions, 

 experimentally demonstrated, Bose explains the diverse 

 movements brought about by the various forces of the 

 environment. 



He thus leads us to the explanation of the movements 

 of tendrils. Whether these be branch-like, i.e. at first 

 uniform and radial, or from the first more or less bifacial, 

 like the leaves, leaflets or stipules which also often develop 

 into tendrils in all these the same reactions to direct and 

 to indirect stimulus appear. Hence it is that the rubbed 

 tendril contracts towards this direct stimulus, and its 

 coiling in this useful direction is thus not a special marvel 

 of natural selection between alternative chances, but is of 

 the nature of all response (though of course the selectionist 

 may then fairly emphasise its special and useful develop- 

 ment). From this simple beginning onwards, all tendril- 

 behaviour may be worked out in detail. 



