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The generally held view that fat accumulation is characteristic of certain classes of algae is based on inadequate evidence. In this investigation the fatty acid, unsaponifiable lipoid, total cell nitrogen, and hydrolysable polysaccharide contents of the following algae have been determined at various stages during growth in pure culture: Chlorella vulgaris, Scotiella sp., Euglena gracilis var. bacillaris, Tribonema aequale, Monodus subterraneus, Navicula pelliculosa, Porphyridium cruentum, Anabaena cylindrica, and Oscillatoria sp. Using the results obtained, the capacities of the algae to accumulate fat have been compared in the following ways: (I) on a percentage dry-weight basis; (2) by means of the differential growth factor relating the fat content of cultures to dry weight of algal material; (3) by consideration of the proportion which fats form of the total reserve material (taken as fat plus hydrolysable polysaccharide) as a function of total cell nitrogen content. Species belonging to the same class have been found to resemble each other in the relative amounts of crude protein, fats, and hydrolysable polysaccharide which they contain. Marked differences in composition between species belonging to different classes have been found, but it is concluded that there are no funda mental differences in the physiological relations of fat accumulation in the algae belonging to the Chlorophycese, Euglenineae, Xanthophyceae, and Bacillario phyceae. Representatives of the Rhodophyceae and Myxophyceae, although they may under certain circumstances have moderately high fat contents, appear to differ in that in them fat accumulation is not associated with low cell nitrogen contents as it is in the other algae examined. No well-defined correlations between the unsaponifiable lipoid and either the fatty acid or total cell nitrogen contents of the algae have been found. Euglena gracilis var. bacillaris has been found to have a rather higher content of unsaponifiable lipoid than the other algae.
Collyer et al. (Sat,) studied this question.