3] 



EFFECT UPON GENERAL FUNCTIONS 



167 



lights employed ; and this is a fundamental matter, for it has 

 been shown, for instance by REINKE ('83 and '84), that, within 

 certain limits, the rate of assimilation increases with the inten- 

 sity of the light (Fig. 44). Even in experiments with the 

 colors of prismatic spectra one must remember that the rays 

 are crowded together at the red end, so that a given length of 

 the spectrum contains more rays at that end than at the other 

 (cf. Fig. 40). 



Later investigations with improved methods have shown 

 quite conclusively that it is especially the rays with X = 0.68 /^, 

 or those very close to the absorption band J9, which are most 



/ 





16 

 1 



FIG. 44. Curve showing the relation between intensity of light (abscissse) and quan- 

 tity of oxygen set free by Elodea canadensis. i indicates the unit intensity of the 

 light from the heliostat. (From REINKE, 'Si.) 



active in assimilation. The methods employed have been most 

 diverse, but they have yielded the same result. TIMIRIAZEFF 

 ('77) studied the assimilative power of the different parts 

 of the solar prismatic spectrum, determining by gasometric 

 methods the quantity of gases decomposed in a given time. 

 REINKE ('84) also used the spectrum, but by means of his 

 spectrophor w^as able to get more strictly monochromatic light, 

 to use more nearly comparable extents of the spectrum, and, 

 especially, to get a more exactly comparable (in this case, 

 optimum) assimilative intensity for each part of the spectrum 

 than his predecessors. (See p. 156.) As the measure of 

 assimilation, REIXKE used the number of gas bubbles set free 



