1148 THE LIGHT FACTOR. ITT. TOLOR CHAP. 30 



Briggs (1929) made yield determinations in light of three colors and 

 obtained the results listed in Table 30. lA. 



Table 30.IA 

 Photosynthesis Yield of Leaves in Colored Light (after Briggs 1929) 



Yield, ml. O2/5OO cal incident light 



Species Yellow light Green light Blue light 



Phaseolus vulgaris 14-17 9-11 7-8 



Uhnus, yellow 8.8 6.5 5.3 



green — 20 12 



Sambucus nigra 8.7 9.3 8.7 



Sambiicus nigra — 19.0 15.0 



These results obtained at light intensities 5-10 times stronger than 

 those used by Warburg and Negelein, show the expected decline in the 

 energy conversion jaeld with decreasing wave length (the experiment with 

 Samhucus is an exception). In other words, the "equienergetic" action 

 spectrum is askew as expected. The decline from yellow to blue is, how- 

 ever, somewhat stronger than could be explained by the quantum correc- 

 tion (the ratio of the yields in yellow and blue is 1.8 to 2.0, instead of 1.4), 

 again indicating a somewhat lower quantum yield in the region of absorption 

 by carotenoids. 



Wurmser (1925) found, for Ulva lactuca, a much higher quantum yield 

 in the green than in the red, and a comparatively low yield in the blue; 

 but these results cannot be considered reliable {cf. page 1118). Gabrielsen's 

 data for Sinapis alba (1935), summarized in Table 30. Ill, (p. 1162) are 

 more significant. The relation between the quantum yields in the red and 

 blue is similar to that found by Warburg and Negelein, and thus allows a 

 similar interpretation. The value in the green — which, in contrast to 

 Wurmser's result, is lower than in the red — may perhaps be taken as an 

 indication that the yellow-green filter used by Gabrielsen transmitted 

 much light absorbed by the carotenoids. 



The only extensive investigation of the quantum yield of photosynthe- 

 sis in a green plant as a function of wave length was carried out by Emerson 

 and Lewis (1941, 1943) with Chlorella pijrenoidosa. They used bands 

 from 5 to 15 m/x wide, obtained by means of a powerful monochromator. 

 Figure 30.1 shows the results. The scattering of the points is indicative of 

 limitations to which the biological "standardization" of cell cultures is sub- 

 ject. Despite this scattering, it appears certain that the yield is approxi- 

 mately constant between 580 and 685 m/x. (The authors believe that the 

 shallow minimum at 660 m/x is real ; for its suggested interpretation, see page 

 1155.) Below 580 mju, the yield declines considerably, reaches a minimum 

 at 490 mju and then recovers. Roughly, the depression of the quantum yield 



