3o8 THE CHLOROPHYLLS AND THE CAROTINOIDS 



In the higher plants the chloroph3lls occur only in the chloroplasts (Chap. 

 VI). The carotene and xanthophylls of leaves are likewise restricted to the 

 chloroplasts. All of these pigments appear to be distributed throughout the 

 proteinaceous ground substance or stroma of the chloroplast. In certain 

 other plant organs such as flower petals these j'ellow pigments often occur 

 in chromoplasts. The chlorophylls and the associated carotinoids are often 

 called the chloroplast pigments. 



The Chlorophylls. — Two different chlorophylls have been extracted from 

 plants: Chlorophyll a, and chlorophyll b. Neither is water-soluble, but both 

 are quite soluble in a number of organic reagents. Chlorophyll a is readily 

 soluble in absolute ethyl alcohol, ether, acetone, chloroform, carbon bisulfide 

 and benzol. Chlorophyll h is soluble in the same reagents, although generally 

 less so. 



Chlorophj'll a is blue-green in solution, and blue-black in the solid state, 

 while chlorophyll b is almost pure green in solution, and greenish-black in 

 the solid state. 



Both of the chlorophylls possess the property of fluorescence. This term 

 refers to the peculiar property possessed by certain substances when illumi- 

 nated of re-radiating light of other wave lengths than those falling upon 

 the substance. Usually the radiated light (fluorescent light) is longer in 

 wave length than the incident light. Chlorophyll a in ethyl alcoholic solu- 

 tion exhibits a deep blood red fluorescence, best seen by viewing the solution 

 in reflected light. Similar solutions of chlorophyll b exhibit a brownish-red 

 fluorescence. 



The Chemistry of the Chlorophylls. — Willstatter and his associates have 

 isolated the chlorophylls in pure form from over two hundred different species 

 of plants and found them to be identical in chemical composition. Both 

 chlorophyll a and chlorophyll b were found in every species studied. They 

 also succeeded in determining the molecular formulas of the two chlorophylls. 

 For chlorophyll a this is C55H7205N4iVIg; for chlorophyll b it is 

 C55H7o06N4Mg. A molecule of chlorophyll a has two atoms more of 

 hydrogen and one atom less of oxygen than a molecule of chlorophyll b. 



Each chlorophyll yields a separate series of degradation products, but one 

 of the products derived from both after mild hydrolysis is an unsaturated 

 primary alcohol which is called phytol (C20H39OH). Phytol makes up 

 about one-third of the chlorophyll molecule. It has a strong aflSnity for 

 oxygen and may be responsible for the reducing action of chlorophyll. 



When ashed pure chlorophyll leaves a residue composed solely of magne- 

 sium oxide. Although iron and other minerals seem essential for the forma- 



