392 CHLOROPLASTS AND CHROMOPLASTS CHAP. 14 



however, that the drops may consist of free phytol, displaced from the 

 chlorophyll molecule by the alcohols used as surface-active agents.) 



Liebaldt's view was shared by Stern (1920, 1921), who considered 

 the fluorescence of chlorophyll in vivo as the most important indication 

 of its state, and observed that nonfluorescent colloidal chlorophyll 

 solutions can be made fluorescent by the addition of a lipide (soap, oleic 

 acid, lecithin, etc.) which converts the colloid into an emulsion with the 

 pigment in true solution in the lipoid drops. Wakkie (1935) found that 

 the presence of sodium oleate prevents the fluorescence of chlorophyll 

 from disappearing upon dilution of a molecular alcoholic solution by 

 water, showing that oleate and chlorophyll associate in colloidal particles, 

 and that this association protects fluorescence from quenching. The 

 oleate-chlorophyll complex can be precipitated from the colloidal solution 

 as a "coacervate" by salting out; the precipitate is fluorescent and 

 birefringent, thus showing a regular arrangement of the molecules. The 

 result of fluorescence experiments was considered by Stern as a decisive 

 evidence that chlorophyll in the cell is dissolved in a lipide. However 

 (as stressed by Hubert, 1936), the absorption peaks of chlorophyll-lipide 

 preparations are situated far on the short-wave side of the absorption 

 peaks of the living cells. This could perhaps be explained simply by a 

 higher pigment concentration in the cell (c/. Chapter 21, Vol. II); but 

 other and perhaps more plausible solutions of the dilemma have been 

 suggested. One was to assume that chlorophyll in the cell is divided 

 into two parts — the first responsible for the absorption spectrum, and 

 the second for fluorescence; another to associate each chlorophyll molecule 

 with both a protein— to explain the position of the absorption bands — 

 and a lipide — to explain the capacity for fluorescence. 



Noack (1925) was the first to suggest that the larger part of chlorophyll 

 in the cells is in a nonfluorescent (protein-bound) colloidal state, while a 

 smaller part forms a fluorescent solution in a lipide. This suggestion 

 was elaborated by Seybold and Egle (1940), who thought the correct 

 position of the absorption band can be achieved only in colloidal systems, 

 while fluorescence can occur only in molecular solution. (The fluorescence 

 of some chlorophyll adsorbates was ascribed by them to the presence of 

 lipoid impurities which dissolve a small amount of chlorophyll.) They 

 prepared a model consisting of a gelatin block containing colloidal 

 chlorophyll. The block was covered by an evaporated layer of a chloro- 

 phyll solution in lecithin-containing ether. This block showed an 

 absorption maximum at 680 m/x characteristic of colloidal chlorophyll, 

 and had a fluorescent surface layer. 



However, there is one drawback to this concept of chlorophyll di- 

 vided between a fluorescent and a nonfluorescent phase : the fluorescence 

 band of chlorophyll in the cell is shifted to the red by about the same amount 



