1905.] Function of Silica in the Nutrition of Cereals. 471 



O'll per cent, of phosphoric acid be taken as the lower limit of phosphoric 

 acid in the straw, that limit is just as much attained in the absence as. in the 

 presence of silica. The greater share of the plant's phosphoric acid trans- 

 ferred to the grain in the latter case comes from the fact that the amount 

 of phosphoric acid assimilated, though increased by the silica, is still not 

 sufficient for the requirements of the plant in the formation of grain, hence 

 the straw continues to be depleted of its phosphoric acid to the lowest limit 

 possible. 



The consideration then of each of the factors submitted to detailed 

 examination — the formation of grain and the migration of nitrogen and 

 phosphoric acid into the grain — leads to the same general conclusion, that 

 an abundant supply of soluble silica renders the barley plant more able 

 to obtain a stock of phosphoric acid from the soil. On the plots therefore 

 which are suffering from phosphoric acid starvation the manuring with 

 sodium silicate acts like a supply of phosphoric acid ; indeed, the plant does 

 actually thereby obtain a larger amount of phosphoric acid. 



Further evidence that the silica acts by stimulating the plant to take up 

 phosphoric acid is derived from water cultures grown in 1904. Three plants 

 of barley were grown in each of four jars, holding about 3 litres of solution, 

 containing the following nutrient salts per litre : — 



Calcium nitrate l - 64 gram. 



Di-hydrogen potassium phosphate . . . 029 „ 



Magnesium sulphate (crystallised)... - 62 „ 



Potassium chlorate 0*71 „ 



with a trace of ferric chloride. 



Growth was vigorous from the first ; the barley plants tillered freely and 

 made a large number of shoots from each grain. On June 7 the nutrient 

 solution was replaced by distilled water, which was changed again on the 8th, 

 and replaced on the 9th by a fresh solution. The new solution contained 

 calcium nitrate, magnesium sulphate, and potassium chloride as before in all 

 the jars ; the phosphoric acid, however, was varied as follows : — 



No. 1. No phosphoric acid. 



No. 2. No phosphoric acid, but 0*146 gramme silica in solution. 

 No. 3. 0-355 gramme phosphoric acid, no silica. 



No. 4. - 355 gramme phosphoric acid, and 0'146 gramme silica in solution. 



It soon became evident that the phosphoric acid and silica, both separately 

 and together, had a ripening effect, which was indicated by an earlier and an 

 increased formation of ears, 



VOL. LXXVII. — B. 2 M 



