612 



ABSORPTION SPECTRA OF PIGMENTS IN VITRO 



CHAP. 21 



than to the chlorophyhin ring system. The frequencies 1045, 1265, 1450. 

 1545 and 1610 cm.-^, on the other hand, seem to belong to chlorophylhn. 



" Strongest bands in italics. 



In considering Table 21.1 and figures 21.1 A and B, one notices the al- 

 ternation of the absorption peaks of the chlorophylls a and b. This rela- 

 tionship was interpreted by Willstatter and Stoll (as well as by Hagenbach, 

 Auerbacher and Wiedemann) as an indication that the two sensitizers sup- 

 port each other in ensuring complete utilization of all wave lengths of the 

 visible spectrum. However, the slight differences in position of the two 

 main bands in the red, and the alternation of low maxima in the yellow and 

 orange, can have but slight influence on the efficiency of light absorption by 

 living plants, as a detailed comparison (at present unavailable) of the ab- 

 sorption spectra of green algae with those of the chlorophyll 6-deficient 

 brown algae will certainly confirm. There is, however, one spectral region 

 in which the presence of chlorophyll b markedly improves the absorption. 

 This is in the blue, between 450 and 530 m/x (cf. chapter 22, page 720). 

 This fact may explain why plants that grow in the shade often contain more 

 chlorophyll 6 than sun plants (cf. page 403). In brown algae, which carry 

 no chlorophyll b, a similar improvement of absorption in the blue is achieved 

 by the presence of fucoxanthol (cf. page 725). 



A much more efficient absorption throughout the visible spectrum 

 could result from the addition, to the yellow-green chlorophyll a, of a pur- 

 ple pigment, with an absorption maximum in or near the middle of the 

 visible spectrum. Nature has provided this type of pigmentation in red 

 algae. These often inhabit the dim regions deep under the sea, and ef- 

 ficient absorption of all radiations that reach them may be a question of 

 life or death for them. For sun-exposed plants, on the other hand, com- 



