CAROTINOIDS IN THE PHANEROGAMS 41 



to the blue solution restored the original yellow color of the solution, 

 although less intense, the blue color reappearing on acidifying again. 

 Sorby (1873) mentioned this reaction for his "yellow xanthophyll." 

 The author 2 has observed that the change from yellow to blue and 

 vice versa can be repeated apparently indefinitely with one of the 

 xanthophylls obtained from plants by Tswett's chromotographic 

 method. 



In his last paper Sclmnck found evidence of the existence in flowers 

 of still another xanthophyll, called Y. xanthophyll, with properties 

 similar to B. xanthophyll, except that it was much less readily 

 extracted from alcohol by carbon disulfide and was accordingly found 

 in the alcohol after the carbon disulfide extractions. Schunck found 

 no evidence of the existence of Y. xanthophyll in his leaf extracts. 

 Kohl (1902e) attempted to harmonize the views of Tschirch and 

 Schunck as well as his own belief that carotin is the principal pigment 

 in the chloroplastids. He recognized the difference between carotin 

 and the xanthophyll proper of Schunck, but apparently did not recog- 

 nize the existence of several of these xanthophylls, as proposed by 

 Schunck. Kohl recognized also the existence of the xanthophyll of 

 Tschirch, which showed no absorption bands, and believed, like 

 Schunck, who proposed no name for the pigment, that it could be 

 extracted from the chloroplastids by hot water, as well as by alcohol. 

 Kohl, therefore, proposed to call Schunck's xanthophyll a xanthophyll 

 and the xanthophyll of Tschirch /? xanthophyll, and expressed the 

 belief that carotin and these two xanthophylls comprised the yellow 

 pigments in the chloroplastids. 



We will now return to a consideration of the investigations leading 

 up to the classification of the carotinoids which prevails at the pres- 

 ent time. Following Borodin, Monteverde (1893) found that the 

 yellow pigments accompanying chlorophyll can be divided into two 

 groups according to their relative solubility in alcohol and petroleum 

 ether, and he was the first to show that this fact offers a very simple 

 means of separating the pigments from each other. Using the pro- 

 cedure of Fremy and Timiriazeff, Monteverde precipitated the chloro- 

 phyll from an alcoholic leaf extract with an excess of Ba(OH) 2 , which 

 carries down with it the carotinoids also, and extracted the yellow 

 pigments from the precipitate with alcohol. Petroleum ether and a 

 few drops of water were added to this yellow solution, and the mix- 

 ture shaken. The liquids soon separated into two layers, each con- 



J Unpublished observation. 



