The lipoid constituents of the phanerogams, especially the serols and carotenoid pigments, have for many years been the subject of intensive study, and the detailed knowledge of them which we now posses contrasts strikingly with lack of precise information concerning the occurrence and character of similar substances among the algae. That the algae contain sterols was first recorded by Willstätter and Page (1914), who noted the existence of a new phytosterol in the brown algaFucus vesiculosus. Montignie (1935) has also recorded the presence of steroid material in certain algae. The first detailed investigation of algal sterols was carried out by Heilbron, Phipers and Wright (1934), who isolated from bothFucus vesiculosusandPelvetia canaliculataa doubly unsaturated sterol of the formula C29H48O, to which the name fucosterol was assigned. This sterol is thus isomeric with stigmasterol, the phytosterol of soya and calabar beans (Windaus and Hauth 1906) and with ostreasterol, the characteristic sterol of oysters (Bergmann 1934). In a further paper Heilbron, Parry and Phipers (1935) showed that fucosterol is also present in the red algaRhodymenia palmataand that it coexists with sitosterol in certain membes of the Chlorophyceae. The algal lipochromes have long been the subject of research, but this has, however, been mostly of a disconnected and empiric nature (cf. Boresch 1932). A wide survey of the field was made by Kylin (1927) who, although not isolating any pigments in the pure crystalline state, reached the conclusion that, apart from carotene which is ubiquitous and common to all classes, each algal class has associated with it its own characteristic lipochrome. The first application to the analysis of alagal lipochromes of the modern methods of phase separation and chromatographic resolution developed by Kuhn and Brockmann (1932a) was described by Heilbron and Phipers (1935). These authors showed that whereas members of the Chlorphyceae continβ-carotene, lutein and possibly taraxanthin, in the phaeophyceae the last two pigments are replaced by fucoxanthin (cf. Willstätter and Page 1914). Further application of these methods has revealed that the so-called "haematochrome" of the Trentepohliae (Cohn 1867; Zopf 1895) consists mainly ofβ-carotene (Heilbron, Lythgoe and Phipers 1935), a result since confirmed by Tischer (1936a). This author has also examined the haematochrome of red Euglenae, and has isolated from it as main constituent a substance of the formula C40H48O4which he has shown to be 4:6:4':6' -tetraketo-β-carotene (I), Isomeric with the crustacean pigment astacene (Karrer and Loewe (1934).