Uchiyama (1907) carried on a variety of experiments with manganese sulphate on several plants on different soils, both in the field and in pots, and found that the compound exercised a favourable action in most cases when applied in appropriate quantities. In summarising his results he stated that both manganese and iron stimulate the development of plants, different plants varying in their susceptibility to the action. Sometimes a joint application of the two salts is the most beneficial, sometimes an individual application is the better, in which case manganese sulphate is generally better than ferric sulphate in its action. The stimulating action of manganese varies greatly with the character of the soil, and the mode of application also affects results. As a general rule the manganese acts best when applied as a top dressing rather than when added together with the manure. Further the stimulating action differs greatly with the nature and reaction of the manurial mixture. Uchiyama concludes that 20–50 kgm. per hectare of crystallised manganese sulphate is a good general amount to apply. Takeuchi (1909) corroborates the statements of the various writers that plants differ in their response to the manganese manuring. Pot cultures, in each of which 8 kgm. soil were similarly manured, received ·2 gm. MnSO₄.4H₂O applied as a solution of 1/100 strength, the controls receiving the same amount of water. The manganese increased the green weight of spinach by 41%, while the dry weight of barley, peas and flax rose 5·3%, 19·4%, and 13·9% respectively above that of the untreated. The control plants of flax were behind the manganese plants in growth and flowering, while barley was the least stimulated of all the test-plants. Other observations seemed to show that Leguminosae and Cruciferae are more susceptible to manganese stimulation than are the Gramineae. III. EFFECT OF MANGANESE COMPOUNDS ON CERTAIN OF THE LOWER PLANTS. The information on this point is exceedingly meagre, possibly because of the diversion of general attention to the higher plants in view of the commercial interests involved. Richards (1897) carried out experiments with various nutritive media with the addition of certain metallic salts, including those of zinc, iron, aluminium and manganese. The fungi tested were _Aspergillus niger_, _Penicillium glaucum_ and _Botrytis cinerea_. His general conclusion was that fungi may be stimulated, though it must not be concluded without further investigation that all fungi react in the same degree to the same reagent, but this conclusion is traversed by Loew and Sawa (1902). These writers state that fungi are _not_ stimulated by manganese, and take this as a proof that the improvement in the growth of phanerogams, induced by manganese compounds, is not due to direct stimulation of the protoplasmic activity, but to some other more obscure cause. IV. PHYSIOLOGICAL CONSIDERATIONS OF MANGANESE STIMULATION.