A large body of work has been done with manganese in soil cultures, but the toxic effect is hardly indicated, possibly because it is less manifest under soil conditions, possibly because the observation of the toxic action has been almost completely overshadowed by the interest in the stimulation observed under the same circumstances. Namba stated that ·5 gm. MnSO₄ added to 8 kgm. Japanese soil exerted a depressing influence on the growth of various plants. The Hills Experiments (1903) indicated some toxic effect. Various soluble and insoluble salts of manganese were added to soil in pots at the rate of 2 cwt. per acre, wheat being sown. On the whole the plants from untreated pots were as good as any with manganese except those that received manganese nitrate or phosphate. Manganese iodide distinctly retarded growth. The plants that grew did well eventually, but development of the ear was greatly or entirely retarded. If the seeds were soaked in the iodide, a concentration of 10% was found to be harmful, 5% allowing normal growth. Similar experiments with barley showed that plants treated with manganese carbonate and sulphate were both inferior to the untreated plants; with iodide less plants were obtained and their development was abnormal. Soaking the seeds in the iodide, even in 10% solution, did not do damage as it did with wheat. The oxides were apparently innocuous, but gave no increase either in corn or straw. Kelley (1909) found that on soils in Hawaii in which excessive quantities of manganese are present (5·61% Mn₃O₄) pineapples do not flourish, but turn yellow and produce poor fruits, and also that if rather less manganese is present (1·36% Mn₃O₄) the pineapples show the toxic effect by yellowing during the winter months, but they recover completely during the hot summer months. Kelley also observed that the deleterious effect is hardly noticeable during the first twelve months of growth, and that after a time a darkening occurs in the colour of the soil, which he attributes to some change in the constitution of the manganese compounds.