42 CAROTINOIDS AND RELATED PIGMENTS 



taining a yellow pigment with distinguishing characteristics. Monte- 

 vcrde found the pigment in the upper petroleum ether layer to be 

 spcctroscopically as well as in other respects identical with carotin 

 and accordingly called it carotin. The pigment remaining in the 

 alcohol layer, on the other hand, was found to be different in many 

 respects and was called xanthophyll, following Gregor Kraus' termi- 

 nology. Monteverde regarded it as not unlikely that this "xantho- 

 phyll" itself consisted of two yellow pigments. In order to separate 

 completely the carotin and xanthophyll the petroleum ether and 

 alcohol layers after separation were shaken with fresh quantities of 

 alcohol and petroleum ether, respectively. On spontaneous evapora- 

 tion of tin- alcoholic xanthophyll solutions Monteverde obtained crys- 

 tals which corresponded exactly in form with the "strohgelben Krys- 

 tallen" described by Borodin. There is some doubt, however, whether 

 the pale yellow crystals observed by Monteverde, and the similar ones 

 observed by Borodin, were actually xanthophyll. Reinke (1885) sev- 

 eral years previously obtained yellow platelets on evaporation of alco- 

 holic solutions of the yellow chloroplastid pigments and found them 

 to be merely phytosterol or a mixture of sterols colored with pigment. 

 It is likely that Monteverde was misled by the same phenomenon, as 

 the great solubility of xanthophyll in alcohol undoubtedly prevents 

 the formation of crystals when one is dealing with the very small 

 quantities of pigment present in Monteverde's solutions. Monteverde, 

 however, described very clearly the difference between the absorption 

 spectra of carotin and xanthophyll, as did Schunck, some years later, 

 between chrysophyll (carotin) and the L. B. and Y. xanthophylls which 

 he separated. Monteverde also described the green coloration, chang- 

 ing to a blue on addition of concentrated HC1 to the alcoholic xan- 

 thophyll solution, a reaction which also characterized the B. and Y. 

 xanthophylls of Schunck, as mentioned in an earlier paragraph. 



Tswett was very quick to recognize the importance of Monteverde's 

 work and the significance of the Kraus method of separation in indi- 

 cating the existence of alcohol-soluble xanthophylls in contrast with 

 benzine-soluble carotin. This investigator's keen appreciation of the 

 significant properties of carotin and xanthophylls is what makes pos- 

 sible today the extension of our knowledge of the distribution of 

 these pigments in all forms of plant and animal matter. Tswett's 

 important observations are accessible to us in a series of papers 

 (1906a, b, c, 1911a) from 1906 to 1911. The last paper is more of 

 the nature of a summary but by reason of its clear-cut statements it 



