46z 



THE QUARTERLY REVIEW OF BIOLOGY 



and yellow constituents in the plastids. 

 Kraus (1871) is given the credit for 

 actually first making a separation of the 

 green and yellow chloroplast pigments. 

 Sorby (1873) claimed that he found two 

 green pigments and five members of the 

 yellow pigments. Tschirch (1887) con- 

 sidered the yellow constituents of the 

 chloroplast to consist of erythrophyll and 

 a group of five xanthophylls. Besides 

 carotin Schunck (1903) thought that the 

 yellow pigments consisted of L, B and Y 

 xanthophyll. Kohl (190Z) attempted to 

 harmonize the views of Tschirch and 

 Schunck as well as his own beliefs. He 

 believed that carotin and only two xantho- 

 phylls comprised the yellow pigments of 

 the chloroplast. 



Monte verde (1893) found that the 

 yellow pigments accompanying chloro- 

 phyll could be divided into two groups 

 according to their relative solubility in 

 alcohol and petroleum ether and was the 

 first to show that this fact offered a very 

 simple means of separating the pigments 

 from each other. Monte verde and later 

 Reinke (1885) attempted to obtain crystals 

 of the pigments. There is considerable 

 doubt as to the exact nature of the crystals 

 which they obtained. Tswett (1906) by 

 this chromatographic method of analysis, 

 using petroleum ether or carbon disulphide 

 solutions of the chloroplast pigments, has 

 shown that at least three and possibly four 

 xanthophylls accompany carotin. He has 

 characterized these pigments at great 

 length and has written much regarding 

 them. It was not until Willstatter and 

 Mieg (1907) isolated the first crystalline 

 xanthophyll and analyzed it that much 

 has been known regarding the real nature 

 of the xanthophylls. Xanthophyll was 

 shown by them to probably have the 

 formula C40H56O2. To the writer's knowl- 

 edge nobody has ever confirmed this 



analysis nor has its accuracy ever been 

 questioned by anybody. Tswett (1910) 

 has expressed the opinion that the xantho- 

 phyll crystallized by Willstatter and 

 Mieg was a mixture of two or three 

 xanthophylls in which his xanthophyll a 

 predominated. Willstatter and Pa 

 (1914) later state that oxidation appears 

 to explain the statements of Tswett 

 regarding his different xanthophylls. 

 Willstatter and Stoll (1913) admit that, 

 their xanthophyll might be a mixture of 

 xanthophylls but at the same time they, 

 regard the different bands found in the; 

 chromatogram as being due to oxidation 

 products of the carotinoids. It seems 

 necessary that those who support state-, 

 ments asserting the presence of more than! 

 one xanthophyll should sooner or laterj 

 furnish better proof than that existing in 

 the literature. Final proof will be the, 

 crystallization or chemical preparation of 

 more than one xanthophyll. 



Evidence obtained by the writer hast 

 shown that some of the bands inTswett's' 

 chromatogram are undoubtedly due to the. 

 oxidation of carotin and of xanthophyll,! 

 for when the pigments are pure and 

 allowed to oxidize these bands appear.' 

 Spectrophotometrical data obtained at the 

 Bureau of Standards also support the con-: 

 tention that there are only two yellow, 

 pigments. Only last year geneticab 

 evidence was submitted which shows that, 

 there are two sorts of carotinoid pigments 

 in maize. One is related to the green 

 pigments in physiological development,) 

 while the other is not thus related. All of 

 the evidence available seems to support 

 the contention that there are only two 

 yellow chloroplast pigments, namely, 

 carotin and xanthophyll, and that the 

 other xanthophylls found in the literature 

 are simply oxidation products of these 

 two pigments. 



