50 PROPAGATION OF PLANTS. 



similar cereals, a,s phosphate of lime (a compound of phos- 

 phoric acid and lime), and it is from such seed or grain 

 that the phosphorus found in the bones of animals is 

 produced, and without which this could not be formed. 

 Sulphates and phosphates are necessary to supply a part 

 of the material forming the protein compounds found in 

 grain. 



Silica is a component part of a large number of plants, 

 and it is a combination of oxygen with a metal-like ele- 

 ment called Silicon. Common flint and the quartz rocks 

 are composed mainly of silica, and the transparent crys- 

 tals of quartz, used for making what are called "pebble" 

 glasses in spectacles and similar purposes, are merely a 

 purer form of the same material. ilica, or silicic acid, 

 is absorbed by the roots of plants largely dissolved in 

 water as silicates, and from this solution it is deposited 

 in the plant-cells, and in widely variable quantities. It 

 is found in great abundance in trees, shrubs, and other 

 w_oody plants, also in the bark or epidermis of the larger 

 grasses Wheat, Rye, Oats, Sorghum, Indian Corn, Bam- 

 boo, and the Tubular Palms ; in fact, it may be termed 

 the great stiffening material of plants. In the Bamboo 

 it is deposited in such large quantities in the cavities of 

 the stems that it is extensively extracted and used under 

 the name of tabasheer by the Hindoos, among whom it is 

 in high repute as a tonic. As found in the Bamboo and 

 some of the other large grasses, it consists chiefly of 

 silica and potash, in the proportion of about seventy 

 parts of silica and thirty of potash. In some kinds of 

 plants, like the common Scouring Rush (Equisetum), 

 the epidermis is almost pure silex, and the ashes of the 

 entire plant are nearly or quite one-half composed of it. 

 Grain raised on land deficient in silica will be weak in 

 the stem and easily blown down when the grain forms in 

 the head or ear. As silica is found in the ashes of plants, 

 we can readily understand how that released by decom- 



