THE LIGHT FACTOR IN PHOTOSYNTHESIS 



1029 



X 



c 

 a) 



20 - 



O 



C 



o 



10 - 



<: 

 o 



400 



550 



450 50Q 



Wave Length in m^i. 



Fig. 5. — Absorption curves in carbon bisul- 

 phide of 1, lutein; 2, zea-xanthin. {Kuhn and 

 Smakula, 60.) 



c'hloropliyll a to chlorophyll 6 averages 2.93 + 0.6; the ratio of 



xaiithophyll to carotene, 1.83 ± 0.5. 



Other pigments occur in smaller and varying amounts, but as yet 



these have not been definitely 30 



identified. "Leaf xantho- 



phyll" is composed of several 



pigments, but the principal 



component from a number of 



plants has been identified as 



chiefly lutein (59). The pro- 

 portion of the carotenes varies 



in different leaves (110), but 



thus far j8-carotene has been 



found in all leaves examined. 



In many leaves it is the main 



component of this group of 



pigments (48). While a- 



carotene also occurs in many 



leaves, it very rarely comprises more than a small fraction of the 



carotene mixture. 



The absorption spectra of the two chlorophyll components have 



recently been determined by Winterstein and Stein (145) in benzene 



solution and by Zscheile (153) in 

 ether solution. Figs. 3 and 4. There 

 is obviously considerable difference 

 in the ratio of the absorption coeffi- 

 cients of the two chlorophylls observed 

 by the two investigators which 

 probably cannot be ascribed entirely 

 to the different solvents used. 



The absorption spectra of lutein 

 and zea-xanthin as determined by 

 Kuhn and Smakula (60) are repro- 

 duced in Fig. 5. 



The absorption spectra of a- and 

 j8-carotene are given in Fig. 6. In 

 this connection it may be stated 

 that the absorption spectra of )3- 



Wcive Lengths in m^ 



Fig. 6. — Absorption curves of 1, a 

 carotene; 2, /3-carotene in 95 per cent 



ethanol. Molar absorption coefficient, carotene and zea-xanthin are very 

 « = -^Y^ log y much alike, as are also those of a- 



{Smith and Miiner, 110.) carotene and lutein It is interesting 



to note that of these pigments the 

 ones with unlike absorption spectra, /S-carotene and lutein, have been 

 found to be the principal carotenoid components. 



