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The occurrence, formation and utilization of polysaccharides, lipids and poly-β-hydroxybutyrate in micro-organisms have been investigated. Bacteria belonging to the genus Arthrobacter were found to accumulate within their cells large amounts (up to 70% of their dry weight) of carbohydrates consisting mainly of polysaccharides. Yeast cells belonging to the Rhodotorulaceae synthesized large amounts of intra-cellular lipids (up to 50%). Some species in addition produced considerable quantities of extra-cellular lipids. The composition of intra- and extra-cellular lipids differed in their component fatty acids and alcohols. Poly-β-hydroxybutyrate was found to occur, in an amount of 30% of the dry cell weight, in the sewage bacterium Sphaerotilus natans; it was also detected in related sheath-forming bacteria. These polymeric compounds were synthesized under more or less similar cultural conditions viz. excess of glucose and deficiency of nitrogen. Lipids and presumably poly-β-hydroxybutyrate may be reserve materials, serving as substrates for endogenous metabolism. The function of polysaccharides is less clear.

It is emphasized, that many constituents of the soil which are essential for the nutrition of plants, may be better estimated by biological than by chemical methods. Some such methods are described, especially those for the estimation of plant-available copper and magnesium, using the mold Aspergillus niger.