70 



FLUORESCENCE SPECTROPHOTOMETRY 



fluorescence contributed by each of the three pigments. A similar 

 dissection of these curves and of five more of the same set with 

 different incident wavelengths was carried out by means of a 

 graphical computer (French et ah, 1954) so that we could calculate 

 the efiFectiveness of each wavelength in exciting fluorescence of each 

 of the three pigments separately. A plot of the effectiveness of different 

 wavelengths in exciting chlorophyll fluorescence is given by the 

 circles in Fig. 20, which also shows the absorption spectra of chloro- 



CO 



LU 



I— 



CC 



o 



(X 



o 



CO 



m 



400 



450 



500 



5 50 



600 



650 



760 



WAVE LENGTH IN MU 

 Fig. 20. Action spectrum for the excitation of chlorophyll a fluorescence in Por- 

 phijridium compared with the absorption spectra of water solutions of phyco- 

 trythriii and phycocyanin and on ether solution of chlorophyll a. (French and 

 Young, 1952.) 



phyll a, of phycoerythrin, and of phycocyanin. There is some fluo- 

 rescence by direct absorption of blue light by chlorophyll a, but 

 strangely enough the points rise along with the phycoerythrin absorp- 

 tion curve in the green part of the spectrum where chlorophyll absorbs 

 weakly. This shows clearly that phycoerythrin is an effective ligh*- 

 absorber for the excitation of chlorophyll fluorescence. Furthermore, 

 the phycocyanin fluorescence, as well as that of phycoerythrin, also 



