FLUORESCENCE OF PIGMENTS in VIVO 



1869 



investigations liave since been described in detail. In amplification of 

 fig. 24.4* (p. 811), French and Young (1952) supplied figures 37C.41 to 

 37C.43. The first one shows the intensities of the fluorescences of chloro- 

 phyll a and of the two phycobilins, excited in Porphyndium by mono- 

 chromatic light of constant quantum flux, as function of wave length. 



600 650 



WAVE LENGTH 



IN MJJ 



Fig. 37C.42. Fluorescence spectra of 

 Porphyridimn excited with monochromatic 

 Hght of different wave lengths (marked on 

 the curves) (after French and Young 1952). 



600 650 700 750 



WAVE LENGTH IN MJLl 



Fig. 37C.43. Analysis of fluorescence 

 of Porphyridium excited by X 530 m^ 

 (after French and Young 1952). 



(The curves are arbitrarily adjusted to coincide at 546 m^.) One notes the 

 almost exclusive excitation of chlorophyll fluorescence by wave lengths 

 below 450 m/x {i. e., in a region of predominant chlorophyll absorption), 

 and simultaneous excitation of all three pigments, w^th almost constant 

 relative intensity, by wave lengths in the region of predominant phyco- 

 bilin absorption, above 480 m/x. Fig. 37C.42 shows the spectra of fluores- 

 cence excited by six different wave lengths. Again, one notices that phyco- 

 bilin fluorescence is not excited by violet light, which is absorbed mainly 

 by chlorophyll, but that fluorescence excited by blue and green light, ab- 

 sorbed mainly by the phycobilins, contains bands of all three pigments. 

 Fig. 37C.43 represents an analysis of the fluorescence spectrum excited, in 



* This figure is by French and Koski; the attribution to Duysens was misplaced 

 and belongs to fig. 24.5. 



