1168 THE LIGHT FACTOR. ITT. COLOR CHAP. 30 



sociated with their higher content of chlorophyll 6 (which permits a better 

 utilization of blue light, 450-500 niju), or with a higher content of carot- 

 enoids (which was indicated by Willstatter and Stoll's figures in Table 

 15. Ill, but was not confirmed, as a general rule, by Seybold and Egle's 

 analysis; cf. Vol. I, p. 414). 



The composition of the pigment system also depends on the color of 

 the light under which the plants were grown. As described in chapter 15 

 (page 130), chlorophyll is more efficiently synthesized by green plants in red 

 light, and the carotonoids in blue-violet light (although these assertions 

 have been contested, and may represent over-simplifications). This may 

 explain why plants have often been found to be most efficient in the light 

 in which they were grown. Elodea plants cultured in red light produced 

 more oxygen in the red, while similar plants grown in blue light gave more 

 oxygen in the blue (Harder, Doring and Simonis 1936, Harder and Simonis 

 1938, and Simonis 1938). Thus, the physiological chromatic adaptation 

 of photosynthesis may be in this case a consequence of the chemical adapta- 

 tion of the pigment system. 



5. Quantum Yield and Action Spectrum of Photosynthesis in Brown 



Algae 



The study of the relation between wave length and photosynthesis in 

 brown algae and diatoms is of special interest because of the presence in 

 these algae of the carotenoid fucoxanthol, which is not encountered in 

 green plants. The distribution of the light absorption by brown algae 

 and diatoms among the individual pigments was discussed in chapter 22 

 (page 723) and illustrated by the (very schematic) figures 22.45A, B and 

 Table 22.IX, all taken from Montfort (1940). For diatoms, we also gave 

 the much more adequate figure 22.46 of Button and Manning (1941). 

 The two reasons why even this figure is not too reliable are: first, the un- 

 certain (and undoubtedly to a certain extent incorrect) assumptions made 

 regarding the "red shift" of the absorption bands in vivo, and, second, the 

 neglect of chlorophyll c. According to Tanada's figure 30. 9B, chlorophyll 

 c adds much to light absorption of pigment extracts from bro^vn algae and 

 diatoms between 450 and 500 mju. The brown color of these organisms 

 in VIVO indicates considerable absorption also farther in the green, from 

 500-550 niM- Part of this absorption may be due to chlorophyll c, but 

 most is probably due to fucoxanthol (to which it has usually been ascribed, 

 cj. page 707). Montfort (1940) discussed the experimental action spectra 

 of photosynthesis in different brown algae and concluded that light ab- 

 sorbed by fucoxanthol is fully utilized for photosjmthesis; but this conclu- 

 sion was not very convincing because of the very primitive experimental 

 approach, which included the use of broad spectral regions, and of light of 



