Effect of Manganese Compounds 83 



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. MnSO 4 added to 8 kgm. Japanese soil exerted a 

 depressing influence on the growth of various plants. The Hills Ex- 

 periments (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 un- 

 treated 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 develop- 

 ment 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 / Q 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 % Mn 3 O 4 ) pineapples do not 

 flourish, but turn yellow and produce poor fruits, and also that if rather 

 less manganese is present (1'36 % Mn 3 O 4 ) the pineapples show the toxic 

 effect by yellowing during the winter months, but they recover com- 

 pletely 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. 



Some interesting observations were made by Guthrie and Cohen 

 (1910) on certain Australian soils. A bowling green that was initially 

 covered with a healthy mat of couch grass developed a number of small 

 patches after about three years growth, on which the grass died off. No 

 reason was apparent for this phenomenon, as the cultural conditions 

 were uniform and to all appearances the soil over the whole area was 

 similar in character. Analyses of soil samples from the dead patches 

 and from the neighbouring healthy parts of the green showed that 

 the chemical composition in both cases was practically the same, except 

 that while no manganese occurred in the soil from the unharmed part, 



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