CAROTINOIDS IN THE PHANEROGAMS 31 



mixture of the same yellow body (partly, it may be, decomposed) with 

 the product of decomposition by acids of the second green body." 

 Stokes never published his method of separation in detail but he gives 

 a hint of its character in a paper in another publication (1864b), in 

 which he states in a discussion of the advantages of a partition between 

 solvents for the separation of various substances, "Bisulphide of car- 

 bon in conjunction with alcohol enabled the lecturer to disentangle the 

 colored substances which are mixed together in the green coloring 

 matter of leaves." 



Stokes was not the only one of the earlier investigators to express 

 the belief that Fremy's pigments were decomposition products. Filhol 

 (1865) also reached this conclusion, as did Askenasy (1867). Filhol 

 (1868) a little later noticed that it is possible to remove the green 

 constituent of crude alcoholic chlorophyll solutions by treating them 

 with animal charcoal insufficient to completely decolorize the solution. 

 A yellow colored solution remained on filtering off the bone-black, the 

 color of which Filhol believed to be due to a pre-existing pigment or 

 pigments associated with the green one. C. A. Schunck (1901), many 

 years later, employed this method of obtaining his xanthophyll group 

 of pigments free from chlorophyll. Schunck's "xanthophylls" included 

 carotin also, so that Filhol's observation was in reality of much more 

 importance than he realized. 



Timiriazeff (1871), studying Fremy's phylloxanthin, also found that 

 alcohol alone would extract the yellow pigment from the barium com- 

 pound thrown down from alcoholic leaf extracts by an excess of 

 Ba(OH) 2 . He preferred to call the yellow pigment xanthophyll, the 

 name previously employed by Berzelius (1837a) from xavSo?, yellow 

 and (f>v\\ov, leaf for the yellow pigment which he extracted from the 

 yellow autumn leaves of the pear tree (Pyrus communis). Sorby 

 (1871b) employed the same term for a group of yellow and orange pig- 

 ments which, with chlorophyll, he believed caused the green color of 

 leaves, and were represented as types by pigments which could be 

 extracted from carrots by CS 2 . 



Notwithstanding the previous observations of Fremy, Stokes, Filhol, 

 Timiriazeff and Sorby, credit is given in most quarters to Gregor 

 Kraus (1872a) for making the first actual separation of the pigments 

 of leaf extracts from one another. Kraus' method is frequently re- 

 ferred to as an "ausschiittlungs" method, for he shook the green 

 alcoholic leaf extracts with benzene and observed that the benzene 

 had extracted the green pigment leaving the alcohol layer a beautiful 



