CAROTINOIDS IN THE PHANEROGAMS 89 



(1872) and Montevcrdc (1893), as well as on his own physico-chemi- 

 cal studies of the leaf pigments. Tswett's theories regarding the 

 chemical relation between the carotin and xanthophyll groups of 

 carotinoids were substantiated by >Yillstiitter and Micg (1907), who 

 isolated the first crystalline xanthophyll and established for it the 

 formula C 40 H 50 (X. Tswett's adsorption method of analysis of the 

 carotinoids in chloroplastids indicates the existence of at least four 

 yellow xanthophylls accompanying carotin in the leaf. The crystal- 

 line xanthophyll isolated by Willstatter and Mieg is probably a mix- 

 ture of two or more of these xanthophylls. The author proposes a 

 colloidal theory to explain the adsorption method of analysis which 

 reveals the several xanthophyll pigments. 



Xanthophylls for the most part are yellow in color, but Monteverde 

 and Lubimenko (1913b) have discovered a red xanthophyll which they 

 call rhodoxanthin. 



The types of carotinoids in etiolated plants and their relative pro- 

 portions have not been studied since the advent of the present caro- 

 tinoid classification and the development of methods for their separa- 

 tion. A review of the older studies indicates, however, that carotin 

 is concerned in the etiolated color, but the evidence is not clear as to 

 the character and extent of the xanthophyll distribution. 



It seems certain that carotinoids are concerned in part in the pig- 

 mentation of naturally yellow and yellow spotted leaves. The types 

 of carotinoids and their relative proportions have not been determined 

 by modern methods. 



The important questions to be answered regarding the yellow chro- 

 molipoids concerned in autumn colorations are: (1) are the yellow 

 autumn pigments merely the carotinoids already present in the chloro- 

 plastids, (2) are these augmented or replaced by other yellow pig- 

 ments closely related to the normal carotinoids but still capable of 

 being differentiated from them, (3) are the yellow autumn pigments 

 entirely new substances? The most recent study of these questions 

 by Tswett (1908c) and Miss Goerrig (1917) shows definitely that the 

 yellow colors are not due to entirely new pigments. It has not been 

 determined with certainty, however, whether or not the chloroplastid 

 carotinoids are slightly modified during the necrobiosis or to what 

 extent new yellow pigments play a part in the autumn colorations. 

 Tswett has concluded that the yellow colors are due entirely to a 

 mixture of slightly modified carotinoids, which he calls autumn xan- 

 thophylls, but which the author believes should better have been 



