CAROTINOIDS IN THE PHANEROGAMS 37 



fact that two crystalline carotinoids in the xanthophyll group have 

 now been isolated from plant forms and their composition determined, 

 the isolation of other known members of this group of pigments still 

 remains to be carried out and their composition and relation to the 

 known members determined. 



Stokes (1864a) is to be credited with the first suggestion of the 

 presence of more than one yellow pigment in chloroplastids, but in 

 spite of the various yellow pigments isolated by Sorby (1873), using 

 Stokes' carbon disulfide procedure, this method could not have led to 

 a true isolation of the various members of the carotinoid pigments 

 which are recognized today. The observation of Dippel (1878) that 

 besides Kraus' xanthophyll a yellow pigment accompanied the cyano- 

 phyll in the petroleum ether layer, could have led to the discovery of 

 the actual existence of two groups of carotinoids. Borodin (1883), 

 however, first demonstrated the existence of more than one yellow 

 chromolipoid when he obtained various forms of crystals from green 

 plants. As already pointed out, these crystals naturally fell into 

 two groups according to their solubility properties, one group, to 

 which Borodin recognized the erythrophyll (carotin) of Bougarel 

 belonged, being very soluble in benzine (petroleum ether) and dif- 

 ficultly soluble in alcohol, and the other group being easily soluble in 

 alcohol but dissolving with difficulty in benzine. These observations 

 of Borodin's are the basis of the classification of the carotinoids which 

 prevail at the present time, considerably extended and supported, of 

 course, by other chemical and physical properties; they also furnish 

 the basis for the separation of the carotinoids into the two groups now 

 recognized, namely, the carotin and xanthophyll groups. This sys- 

 tem of classification is the only logical one, as has been pointed out by 

 Tswett and proven by the chemical analyses of members of each group 

 by Willstatter and his co-workers. Before reviewing the history and 

 evidence in favor of this classification and the proof of the existence 

 of individuals in the group, it should be stated that the plurality of 

 yellow chromolipoids in chloroplastids has been recognized by other 

 investigators who have proposed other systems of classification. These 

 latter studies will be reviewed first. 



Tschirch found proof of the existence of more than one yellow 

 chromolipoid in his well-known series of spectroscopic studies of 

 chlorophyll. In his first papers Tschirch (1884, 1885, 1887) con-, 

 sidered the yellow constituents of the chloroplastid to be erythrophyll 

 (adopting Bougarel's terminology) and a. group of five xanthophylls, 



