The colour of the chromoplasts in the Chrysophyceae varies from a greenish yellow to a golden brown. Klebs (1892) described this colour as being due to a special pigment which he called ‘chrysochrom’. Gaidukov (1900) made an acetone extract of a dense bloom of Chromulina rosanoffii (Woronin, 1880) Biitschli filtered from the tanks in the cold glasshouses of the Botanic Gardens in St Petersburg. He found a water soluble pigment which he called ‘phycochrysin’ together with ‘chrysochlorophyll’ and ‘chrysoxanthophyll’. Most authors have since questioned the existence of special pigments in the Chrysophyceae (Fritsch, 1937; Smith, 1938). Carter, Heilbron & Lythgoe (1939) analysed extracts of an incrustation of Apistonema carteri, Thallochrysis litoralis and Gleochrysis maritima (identified by F. E. Fritsch) found on the chalk cliffs at Folkestone, and identified β-carotene, fucoxanthin and lutein, using calcium carbonate as adsorbent in their analysis. Heilbron (1942) later drew attention to the fact that these pigments are present in the Bacillariophyceae but not in the Xanthophyceae, throwing doubt on Pascher's view of the close relationship of all three groups. We now know that it is not lutein but diadinoxanthin that is present in the Bacillariophyceae (Strain, Manning & Hardin, 1944). Seybold, Egle & Hülsbruch (1941) then showed that the chlorophyll present in Hydrurus foetidus and Chromulina rosanoffii was chlorophyll a, apparently without other chlorophylls. Seybold (1941) has commented further on the singular occurrence. and implications of chlorophyll a alone, and this has been recently discussed by Allen (1958). In recent years our knowledge of the pigments of the algae has been greatly advanced by Strain and his colleagues (Strain, 1958) but, while the pigments of the Xanthophyceae and Bacillariophyceae have been examined with the improved techniques now available(Pace, 1941; Strain, Manning & Hardin, 1943, 1944; Strain, 1958), those of the Chrysophyceae have not.