/ 



- 8 - 



reacti-ve solvents. They were preferentially soluble in fats, and, there- 

 fore, their extraction from plant material required the use of fat sol- 

 vents. With fresh plant material, it was necessary to employ solvents 



' that also removed the water of the plant tissue as, for example, methanol, 

 ethanol, or acetone. With freshly dried plant material, water-immiscible 



'^solvents, such as carbon disulfide, benzene, ether and petroleum ether 

 could also be employed as extractants. 



Multiplicity of the Qhloroplast Pigments 



For a long time, there was thought to be but a single pigment in 

 photosynthetically active plants i namely, the green of leaves or chloro- 

 phyll. But as new separatory methods were applied to the extracts of 

 various plants, several green pigments and many yellow ones were found. 

 Both in plant extracts and in the chloroplasts themselves, the green 

 pigments obscure the yellow ones. The green pigments are called chloro- 

 phylls'^'^. The yellow pigments are members of a large group of polyene 

 pigments known as carotenoids. These chloroplast carotenoids are sub- 

 divided into two subgroups, the carotenes or polyene hydrocarbon caro- 

 tenes or polyene hydrocarbon carotenoids, typified by the carotenes of 

 carrot roots, and the xanthophylls or oxygen derivatives of the caro- 

 tenes, typified by the xanthophylls or leaf yellow of autumn leaves7>°> 

 9,10,11,12^ Many pigments, representative of these three groups, have 

 now been found in various plants, particularly in the algae-^. Each 

 kind of plant usually contains one or two chlorophylls, several xantho- 

 phylls and one or more carotenes". 



A very large n\unber of the carotenoids, especially the xanthophylls, 

 occur in yellow specialized plant organs such as yellow flowers, fruits. 



