26 



THE METABOLISM OF ALGAE 



Chlorella/^ Uha and Monostroma^^^ light absorbed by 

 carotenoids appears to be partly, but not entirely, utilized 

 in photosynthesis. In Chroococcus, however, light absorbed 

 by carotenoids seems to be for the most part unavailable 

 for photosynthesis. "^"^ Carotenoids sometimes occur else- 

 where in the protoplast than in the chromatophore and are 



/OO 



THALLUS ABSORPTION 

 ACTION SPECTRUM 



400 440 



480 520 560 600 640 

 WAVE LENGTH IN Mju 



680 720 760 



FIG. 



6. Absorption and action spectra of Coilodesme californica. 

 The action curve for photosynthesis, corrected to relative 

 rates for equal numbers of incident quanta, has been made to 

 coincide with the absorption curve at 675 m/ix. The relatively 

 minor divergence between the two curves in the region 500 

 to 560 m/x suggests that light absorbed by fucoxanthin is 

 effective in photosynthesis (after ref. 139). 



presumably then inactive in photosynthesis and it may be 

 that within the chromatophore spatial arrangements exclude 

 some carotenoid molecules from participation in active 

 light absorption. Another possibility is that certain types 

 of carotenoid are able to absorb light for use in photo- 

 synthesis but that others are quite inactive in this way. 



Because their main absorption bands are widely separated 

 from those of the chlorophylls, the phycobilins provide 



