60 CAROTINOIDS AND RELATED PIGMENTS 



before it was definitely known that several yellow ehromolipoids exist 

 in the green leaf. For example. Gregor Kraus (1872c) believed that 

 the yellow autumn pigment was due in part to his yellow xanthophyll 

 and in part to a yellow water-soluble pigment. Sorby's (1871a, b) 

 idea that autumn coloration is due to varying mixtures of xantho- 

 phylls, erythrophylls and chrysotannins is not far different from 

 Miss Goerrig's remit conclusion when one is acquainted with the par- 

 ticular properties of Sorby'< piumrnt groups. Sorby's xanthophylls 

 are our present carotinoids; his erythrophylls are acknowledged to be 

 our red anthocyanins (they were characterized by being strikingly 

 affected in color by alkalies and acids ) ; and his chrysotannins, which 

 he believed increased during the autumnal color changes, were indefi- 

 nite water-soluble yellow pigments with acid properties (related to 

 tannic acid) which readily deepened in color on oxidation. Miss Goer- 

 rig found abundant quantities of a yellow pigment in autumn leaves, 

 which could be extracted with dilute acetone. Saponificatioo of the 

 extract greatly intensified the color, and the unsaponified pigment 

 could not be extracted from the dilute acetone by ether. There also 

 seems to be little reason to doubt the identity of Sorby's chrysotannin 

 and Mi-s Goerrig's unnamed yellow water-soluble pigment with the 

 so-called aiitunin-xantliin which Staats (1895) extracted with alcohol 

 from the yellow autumn leaves of the linden (Tilia) , beech (Fagux), 

 ash (Fraxinm) and red oak (Quercw n/hra), and which he obtained 

 in the form of 'a red crystalline water-soluble potassium salt. Staats 

 ascribed the autumn pigmentation solution to this coloring matter, 

 but in this he was, of cour-< . mi-taken. The alcoholic extract of the 

 oak leaves first turned irreen and then yellow with the precipitation of 

 the potassium salt, when treated with KOH, confirming the observa- 

 tion of Macairc-Prinsep (1828), mentioned above, on extracts from 

 autumn poplar leaves. The explanation of this interesting color reac- 

 tion of autumn leaves is not apparent. 



Carl Kraus (1875) also ascribed the autumn coloration to more 

 than one pigment, naming two, xanthin, especially, and also xantho- 

 phyll. To explain briefly his terminology it may be stated that his 

 xanthophyll was practically the Gregor Kraus xanthophyll in that 

 author's alcohol-benzene separation, Carl Kraus characterizing it 

 further because of its change to a blue pigment on treatment with 

 acid (this is either the phylloxanthine reaction of Fremy (1860), or 

 the xanthophyll |3 color reaction of Tswett (1911a)). The xanthin of 

 Carl Kraus, however, is undoubtedly carotin, since he found it in the 



