[Illustration: Fig. 17. Curve showing the mean value of the dry weights of ten series of barley plants grown in the presence of manganese sulphate and nutrient salts. (Feb. 5th–March 29th, 1909.)] [Illustration: Fig. 18. Photograph showing the action of manganese sulphate on barley plants grown in the presence of nutrient salts. (Feb. 5th–March 29th, 1909.) 1. Control. 2. 1/10,000 manganese sulphate. 3. 1/100,000 „ „ 4. 1/1,000,000 „ „ 5. 1/10,000,000 „ „ 6. 1/100,000,000 „ „ ] [Illustration: Fig. 19. Photograph showing the action of manganese sulphate on pea plants in the presence of nutrient salts. (Oct. 2nd–Dec. 20th, 1912.) 1. Control. 2. 1/5,000 manganese sulphate. 3. 1/10,000 „ „ 4. 1/25,000 „ „ 5. 1/50,000 „ „ 6. 1/100,000 „ „ 7. 1/250,000 „ „ 8. 1/500,000 „ „ 9. 1/1,000,000 „ „ ] (_b_) _Stimulation in soil cultures._ Roxas carried out pot experiments with rice in soil to which was added varying proportions of manganese sulphate, with and without the addition of nutrient salts of ammonium, potassium, and calcium. The criterion of stimulation was the length of the growing leaves as measured daily, a strength of M/1000 MnSO₄ (M = molecular weight) giving a favourable result. In the Hills Experiments (1903) an increase of produce was obtained with wheat by manuring with manganese phosphate, chloride, sulphate, or oxide (MnO₂), while an increase of straw was gained with nitrate, though this compound decreased the yield of corn. With barley no evidence of stimulation is set forth for any compound, except that the root growth was improved by the addition of manganese iodide, in spite of the general unfavourable action this substance exerted upon germination and growth. Bertrand (1905) whose work will later be considered in detail, experimented on arable land, adding quantities of manganese sulphate (?) equivalent to about 1·6 gm. Mn to each square metre, growing oats from February to May. Increase of weight was found in the plants growing on the manganese plots, the differences in favour of manganese being For total crops 22·5%. „ grain only 17·4%. „ straw only 26·0%. A certain alteration in the quality of the grain was also noted from the manganese plots, the weight per hectolitre exceeding that from the untreated plot, the % of water and of total nitrogen being somewhat lower than that from the untreated, while the ash and the quantity of manganese present was the same in the grain from both plots. Bertrand suggested that these results might indicate a new line to follow in the study of the causes of the soil fertility.