GENERAL DISTRIBUTION OF CAROTINOIDS 21 



Non-car otinoid Plant Pigments 



Carotinoids, however, are not the only yellow and orange colored 

 pigments found in the plant and animal kingdoms, which fact must 

 not be lost sight of in the examination of plant and animal products 

 for the presence of carotinoid pigments. 



Although all plant pigments have a hydrocarbon nucleus there are 

 only a few yellow to red hydrocarbons known which are not carotin- 

 oids. They are the acenaphtylene of Behr and van Dorp (1873), 

 Blumenthal (1874) and Graebe (1893), the di-biphenylenathene of de 

 la Harpe and van Dorp (1875) and Graebe (1892), the fulvenes of 

 Thiele (1900a), the cinnamylidenindene of Thiele (1900b), and the 

 rubicene of Pummerer (1912). Each of these is discussed more fully 

 in Chapter IX, in connection with the probable constitution of carotin. 



Among the naturally occurring yellow vegetable pigments which 

 contain carbon, hydrogen and oxygen, but which have no relation to 

 the xanthophyll group of carotinoids, two especially well defined 

 groups are known, namely, the xanthones and the flavones. Five 

 xanthones are known, (1) Cotoin, C 13 H 12 4 , (2) Euxanthone, 

 C 13 H 6 (OH) 2 2 , (3) Maclaurin, C 13 H 5 (OH) 5 0, (4) Datiscetin, or 

 di-methyl-tetraoxyxanthone, C 15 H 12 6 , and (5) Gentisein, C 13 H - 

 (OH) 3 2 . The structural constitution of each of these pigments is 

 known. A much larger number of flavones are known, all of which 

 are characterized by the common nucleus, (3-phenyl-benzo-y-pyrone. 

 Many of the natural pigments occur as glucosides and are regarded 

 as the chromogens from which anthocyanins are derived (Wheldale, 

 1916). Some of the more interesting members with a yellow color 

 are (1) Luteolin, which is not to be confused with the carotinoid, 

 Eteolin, but which is 1,2, 3, 4-tetra-oxyflavon ; and (2) Gossyptin, the 

 yellow dye in the yellow flowers of the Indian cotton (Gossypium 

 herbaceum) , occurring there as a glucoside. No doubt the yellow 

 color of cottonseed meal is due in part to Gossyptin, which can be 

 extracted from cotton flowers with hot alcohol. The pure pigment 

 exists as glistening yellow needles. 



Besides the xanthones and flavones other yellow pigments are found 

 in plant parts, among which may be mentioned chrysophanic acid, a 

 methyl di-hydroxy anthracene whose solution in alcohol, ether, ace- 

 tone, benzene, chloroform or petroleum ether will dye animal tissues a 

 deep yellow color. Of special interest in this connection is the yellow 

 pigment of the seeds of annatto (Bixa orellana), called bixin or 



