698 



LIGHT ABSORPTION BY PIGMENTS IN VIVO 



CHAP. 22 



Timiriazev (1872), in an early discussion of the effect of scattering on 

 the spectrum of leaves, suggested that scattering may not only broaden 

 the absorption bands, but also shift their maxima. However, the attribu- 

 tion of the "red shift" to scattering is not permissible, as shown, e. g., by 

 the return of the red band to the position it occupies in solution, after soak- 

 ing the leaves with ether, or immersing them in boiling water (fig. 22.34) 

 (Willstatter and Stoll 1918, Seybold and Egle 1940, Seybold and Weiss- 

 weiler 1942). These treatments do not dissolve the pigments, and do not 

 make the tissues more homogeneous; they merely destroy the association 



o 



z 

 < 

 q: 



400 



500 600 



WAVE LENGTH, m/i 



Fig. 22.34. Effect of boiling and immersion 

 in ether on transmission spectrum of a Parie- 

 taria leaf (after Seybold and Weissweiler 

 1942). 



700 



Q. 



q: 

 o 



m 



< 



670 680 690 700 

 WAVE LENGTH, m>i 



Fig. 22.35. Absorption spectra 

 of single Protococcus chloroplasts 

 (after Albers and Knorr 1937). 



of chlorophyll with proteins and lipides. Drying, on the other hand, 

 which changes the scattering of light by leaves to a much larger extent 

 than immersion in hot water, does not affect the position of the red band 

 maximum (Seybold and Egle 1940). 



The conclusion that the position of the red absorption peak in the liv- 

 ing cell is not affected by scattering, is confirmed by determinations of the 

 absorption spectra of single Euglena cells (Baas-Becking and Ross 1925), 

 and of single chloroplasts (Albers and Knorr 1937). Figure 22.35 shows 

 that the absorption maximum of single Protococcus chloroplasts lies close 

 to 680 m/x, i. €., in the same region as in whole plants. 



Scattering effects must be weaker than in leaf spectra not only in the 

 spectra of single cells, but also in those of cell suspensions. Several such 

 spectra were reproduced above (cf. figs. 22.21 and 22.22 for Chlorella, 



