LIGHT ABSORPTION BY PIGMENTS in VWO 1847 



of Chlorella. In Noddack's measurements, however, scattering was not eliminated 

 (as it was supposed to be in Barer's experiments), Ijut merely excluded from measurement; 

 therefore, the possibility of the scattering increasing significantly the true absorption in 

 the minima (by the so-called "detour factor," cf. chapter 22) could not be ruled out. 



Barer noted that the position of the main red peak varied, in different 

 green algal suspension, between 675 and 680 myu, and that of the main 

 violet peak, between 435 and 440 m/i. 



New absorption bands Avere foinid by Barer, in Chlorella, at 385 and 

 340 m.n, probably corresponding to the solution bands of chlorophyll a 

 at 380 and 330 m^, respectively (c/. fig. 21.3). In Closterium, an absorp- 

 tion band was noted at 620 myu, of which only a slight indication can be 

 found in the Chlorella spectrum ; it was suggested that it is the equivalent 

 of the 612.5 m^c band of chlorophyll a in solution (fig. 21.1). Closterium 

 spectrum showed no evidence of the 645 m/x band, which would indicate 

 the presence of chlorophyll h. 



The absorption peaks of green algae at 480 and 490 m/x, presumably' due to caro- 

 tenoids, were noted by Barer to become progressively more pronounced in the transition 

 from yellow, through yellow-green, to green Chlorella strains, indicating a parallel 

 increase in the contents of chlorophyll and the carotenoids (unless the 480-490 m/x 

 band is attributed — at least in part — to chlorophyll b\). 



(h) Two Forms of Chlorophyll in vivof 



Krasnovsky and Brin (1948) suggested that chlorophyll is present in 

 leaves in two different forms. The less abundant form, with a band at 

 665-670 mn, they supposed to be "non aggregated," but bound to a lipide, 

 or lipoprotein. It was also supposed to be fluorescent and photochemically 

 active. The main amount of chlorophyll, responsible for the band at 677- 

 678 mil, was supposed to be in an "aggregated" (colloidal), nonfluorescent 

 and photochemically inactive form — a kind of "chlorophyll reserve." 

 This hypothesis is very similar to that propounded earlier by Seybold and 

 Egle (c/. p. 818) . The argument used on pp. 746 and 819 against the latter 's 

 assumption that two different forms of chlorophyll account for the main 

 absorption band and the fluorescence band in vivo — the approximately 

 equal shifts of both bands from their positions in solution — was considered 

 by Krasnovsky and Brin to be unconvincing because, in their opinion, 

 self-absorption of fluorescence could have caused an apparent shift of the 

 fluorescence band toward the longer waves. (The fluorescence band, 

 corresponding to the absorption band at 665-670 m/x of the "nonaggregated" 

 photoactive chlorophyll, could be located under the absorption peak of the 

 "aggregated" form at 677-678 m/x, and distorted by absorption so as to 

 show an apparent peak at 680 m/x. French's fig. 37C.45 shows this type 

 of shift.) 



