10 THE CHEMISTRY OF THE FARM. 



the plant little is known. Phosphoric acid and potash are 

 undoubtedly the most important of the ash constituents ; 

 they are always found concentrated in those parts of the 

 plant where cell growth is most active, as, for instance, in 

 the layer (cambium) between the wood and bark of a tree, 

 and are abundantly stored up in the seed. 



Silica was long supposed to be an essential constituent 

 of wheat, barley, and other similar plants, and to be the 

 ingredient on which the stiffness of their straw chiefly 

 depended. It has been shown, however, that maize may 

 be successfully grown without any supply of silica, and 

 with no perceptible difference as to the stiffness of the 

 stem. The grass growing on peat bogs contains scarcely 

 any silica, though silica is abundant in ordinary hay. 



Germination. — The seed is a storehouse of concentrated 

 plant food, intended to nourish the germ till the root and 

 leaf are developed. In the seeds of the cereals, and of many 

 other plants, the chief ingredient is starch. Another class 

 of seeds, of which linseed and mustard-seed are examples, 

 contain no starch, but in its place a large quantity of fat. 

 A seed generally contains a considerable amount of albu- 

 minoids ; its ash is rich in phosphoric acid and potash. 



For germination to take place, moisture, oxygen, and a 

 suitable temperature are necessary. Under these con- 

 ditions the seed swells, oxygen is absorbed, a part of the 

 carbonaceous ingredients is oxidised, heat is developed, 

 and carbonic acid evolved. During these changes the 

 solid ingredients of the seed gradually become soluble ; 

 the starch and fat are converted into sugar ; the albu- 

 minoids are converted into amides — as for instance aspara- 

 gine, probably also into peptones. With this supply of 



