THE PHOTOTROPHIC ASSIMILATION OF CARBON 2$ 



between this efficiency curve and those for the distribution 

 of absorption among the pigments /« vivo indicate that Hght 

 absorbed by fucoxanthin is utiUzed in photosynthesis with 

 about the same efficiency as that absorbed by chlorophyll. 

 Thus at 550 m/f, where some 80 per cent of the light 

 absorption is by fucoxanthin, there is no decline in quan- 



/oo 



CHLOROPHYLLS 



FUCOXANTHIN 



OTHER 



CAROTENOIDS 



400 



450 



600 550 600 



^AVE LENGTH IN M/A 



650 



70O 



FIG. 5. Curves showing the estimated distribution of light absorp- 

 tion among the different groups of pigments in live cells of 

 Navicula minima (after ref. 280). 



tum yield as compared with that at 650 m/« where 100 per 

 cent of the light is absorbed by chlorophylls^ Light absorbed 

 by other carotenoids, however, does not appear to be avail- 

 able for photosynthesis. 2^*^ 



Fucoxanthin appears to be effective in the same way in 

 Phaeophyceae, comparison of the action and absorption 

 spectra for Coilodesme (Fig. 6) showing a high photosyn- 

 thetic activity in the region 500 to 560 mfx where absorption 

 is chiefly by this pigment.^^^ In green algae such as 



