1174 



THE LIGHT FACTOR. III. COLOR 



CHAP. 30 



yield dips by about 20% between 520 and 475 ibm (we recall that a minimum 

 of efficiency was found in this region also for Chlorella and Chroococcus) . 

 The yield rises somewhat further in the violet, but declines again toward 

 the ultraviolet, its value at 400 mju being about 30% below the maximum. 

 This 7 = /(X) curve must be compared with the curve showing the ab- 

 sorption by the several pigments in extract from these diatoms (fig. 30. 9B), 

 and with the curve (fig. 30.9D), derived from it, showing the contribution 

 of each pigment to the total absorption by the cells. The first figure shows 

 chlorophyll a, chlorophyll c, and fucoxanthol, as the major components. 



100 



o 



a: 

 o 

 (/) 



CD 



< 



80 



60 



u. 40 

 o 



z 



UJ 



o 

 cc 



UJ 



CL 



20' 



400 



450 500 550 600 



WAVE LENGTH, m/x 



650 700 



Fig. 30.9D. Curves showing the estimated distribution of Uglit 

 absorption among pigment groups iii live cells of 'N . minima as a 

 function of wave length. 



Neofucoxanthol (c/. chapter 37), /3-carotene and an unidentified carotenol 

 (possibly diadinoxanthol) also were identified; their absorption is lumped 

 together under the heading of "other carotenoids." 



In deriving, from the spectra of pigments in vitro, their contribution to 

 total absorption in vivo, corrections for scattering, band shift, and band 

 broadening, must be applied. The unsatisfactory state of this problem 

 was discussed in chapter 22. Tanada made one improvement in the pro- 

 cedure: he found that most of chlorophyll c and some fucoxanthol can be 

 extracted with 65% methanol, leaving practically all chlorophyll a in the 

 cells; the spectrum of the residue could tlien be used to locate the position 

 of the blue-violet absorption peak of chlorophyll a, and of "other caro- 

 tenoids" in the cell. The red shift of the blue-violet band of chlorophyll a, 

 determined in this way, was 8 mju; that of "other carotenoids," 20 m^i. 



