100 CAROTINOIDS AXD RELATED PIGMENTS 



brown algae, as Tswett concluded. The question still remains open, 

 however, as to whether more than one xanthophyll is present. 



The Rhodophyccac. These plants, commonly known as the red sea- 

 weeds, are, like the brown algae, found mostly in salt waters, only a 

 few inhabiting fresh water. Both forms, fortunately, have been ex- 

 amined for carotinoids. The plants are especially abundant in the 

 tropic oceans and in the temperate regions at lower depths. Several 

 hundred species have been described. The dried thallus of Chondrus 

 crispus forms the carragheen, or dried moss which is used for its gela- 

 tion properties. Various species of these plants are the source of agar- 

 agar. The thallus of the Rhodophyccae is abundant in pigment and 

 may be red, violet or purple, but rarely green. The characteristic 

 pigment, however, never appears to be carotinoid. Some chlorophyll 

 appears to be present, but the chief pigment is a protein-like material 

 or is combined with such (Kylin, 1911 1, and is known as phyco- 

 ery thrill. 



The red algae, however, do not lack carotinoids. Those in which 

 the chromolipoids have been demonstrated are given in Table 9. The 

 investigations upon which our knowledge of the carotinoids in the red 

 algae depends may be summarized as follows. 



Sorby (1873) appears to have first called attention to the presence 

 of yellow pigments in this class of plants, when he was able to demon- 

 strate the presence of xanthophyll in Porphyra vulgaris. It will be 

 recalled from the summary of Sorby 's work given in Chapter II that 

 his "xanthophyll" corresponds in properties with the xanthophyll a 

 of the higher plants as revealed by Tswett's chromatographic analysis, 

 and also to the chief properties of the crystalline xanthophyll isolated 

 from green plants in Willstatter's laboratory. 



Reinke (1876) extracted Batrachospermum moniliforme with hot 

 alcohol, and obtained a yellow extract which gave up its pigment to 

 benzene. This result indicates carotin in the light of our present 

 knowledge of the relative solubility properties of the carotinoids. 



Nebelung (1878) examined the effect of alcohol and petroleum ether 

 as solvents for the pigments of several fresh water Rhodophyceae, and 

 found that a yellow pigment (or pigments) could be extracted. 



Hansen (1893) applied his method of separating green and yellow 

 pigments to the alcoholic extracts of a number of red algae. He 

 found that green and yellow fractions could be obtained by treating 

 the extracts with alkali and shaking with ether. He regarded the 



