PHYSIOLOGICAL STUDIES 67 



Emerson and Lewis (1942) have shown in Chroococcus that 

 light absorbed by phycocyanin is almost as effective as that 

 absorbed by chlorophyll. In the red algae Haxo and Blinks 

 (1950) have shown that light absorbed by phycoerythrin 

 appears to have an even greater efficiency than light absorbed 

 by chlorophyll. This however is probably due to the fact 

 that in the species studied light absorbed by chlorophyll 



fO 



400 



480 sea 640 



Wavelength of light 



m/^ 



FIG. 4. 1 1 . Quantum efficiency of Chlorella pyrenoidosa as a function 

 of the wavelength of light. (After Emerson and Lewis.) Varia- 

 tion in data shown by vertical lines; band width in different 

 spectral regions by horizontal lines. 



itself w^as used with poor efficiency, thus raising the ques- 

 tion, not yet fully answered, as to whether all of the 

 chlorophyll in a cell is equally efficient photosynthetically. 



Hence there is good evidence that the light absorbed by 

 pigments other than chlorophyll can be utilized for photo- 

 synthesis. Since chlorophyll a is the only pigment common 

 to all photosynthetic organisms it has been suggested that it 

 is the only pigment which directly donates energy to the 

 photosynthetic reactants, the other pigments first trans- 

 ferring their excitation energy to it. This may be correlated 



