XXXI.— THE RELATION BETWEEN THE QUANTITY OF 

 LIGHT AND THE INDUCED PHOTOTROPIC 

 CURVATURE 



By 



Sir J. C. BosE, 



Asftisted by 

 SURENDRA Chandra Das, m.a. 



I SHALL in this chapter describe experiments in support 

 of tlie important proposition that the intf.nsity of phototropic 

 action is dependent on the quantity of incident light. The 

 proportionality of the tropic effect to the quantity of light 

 will be found to hokl good for the median range of stimu- 

 lation ; the deviation from this proportionality at the two 

 ends of the range of stimulation — the sub-minimal and supra- 

 maximal — is, as we shall fin<l, capable of explanation, and 

 will be fully dealt with in the next chapter. 



The quantity of light incident on the responding organ 

 depends : (1) on the intensity of light, (2) on the angle of 

 inclination or the directive angle* and (3) on the duration 



* The directive angle Q is the angle of inclination of the rays of light to 

 the responding surface. The angle Q is complementary to the angle of incidence i 

 in optics. Sin — Cos i. 



