1) In the experiment with rice plants by the method of sand-culture, the addition of colloidal silica increased the efficiency of tricalcium phosphate markedly and that of acid phosphate slightly. 2) The increase of the phosphoric acid-content in the plants depended upon the quantity of colloidal silica supplied. 3) The contents of crude ash and silica in the straws and in the mixtures of husks and chaff increased with the increase in the supply of colloidal silica. 4) In the unhulled rice, the content of phosphoric acid, and its percentage for the total phosphoric acid in the plants, increased with the increase in the supply of colloidal silica. From the results obtained, it seems that silica has the function of facilitating the transportation of phosphoric acid in the plant body. 5) The greate r the supply of colloidal silica, the greater was the increase of silica observed in the plants. 6) There was no difference b etween colloidal silica and so called precipitated silica in their beneficial action upon the efficiency of phosphates. 7) The effect of colloidal silica on the decomposition o f tricalcium phosphate, with or without nutrient salts, was found to be negative in the laboratory experiment.
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