1846 



SPECTROSCOPY AND FLUORESCENCE OF PIGMENTS CHAP. 37C 



and 1.36 for (green) Chlorella, in good agreement with the earher data in 

 table 22.VII. 



The relative transmission in the /ar red also was, in Barer's curves, lower 

 than in earher measurements — e. g., in (green) Chlorella the ratio of optical 

 densities at 720 and 675 mju was about 0.4, as compared with about 0.2 

 in fig. 22.22. This difference, too, is opposite in sense to what one would 

 expect from an effective elimination of scattering! The problem of the 

 true absorption curve of algal cells thus seems to need further attention. 



ed. These roquireixtonts are met by 



actiu 



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 iglih 

 i1 \oi 

 V o I 

 disti 

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ex|)('i'iM- --^ ■ vd.v^. full 

 ^. iU^Mvihoii elsewhere. 



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ion for 



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Fig. 37C.28. Removal of scattering in a bacterial suspension by the use of sus- 

 pension medium with properly adjusted refractive index (Barer 1955). 



One particular point, which needs clarification, is to what extent scattering 

 can explain the high apparent absorption by cells in the green and in the 

 far red. We will see below (section 6 A) that, according to Duysens (1954), 

 ordinary Rayleigh scattering can account for both the shallowness of the 

 "green trough" and the existence of a "red tail" in the transmission curve; 

 but that the observations of Latimer (1954) indicate the occurrence of a 

 strong selective scattering on the long-wave side of the main absorption 

 bands, which is bound to contribute to the diminution of transmission, par- 

 ticularly in the far red. 



Sharp selective scattering bands are associated not only with the main 

 absorption bands of chlorophyll, but also with those of the carotenoids, 

 although the latter are merely ripples in the absorption curve of live 

 Chlorella cells. 



On p. 709, we noted that the dips in the green and in the red were as shallow in 

 Noddack's "pure absorption" curve as in Emerson's "absorption + scattering" curve 



