SILICA. 47 



Soluble silica is indispensable to the growth 

 of grasses and the straw of cereals, and forms 

 the shining outer sheath of these plants. It is 

 very abundant in the hard external coating of 

 the "Dutch rush used for polishing. 



Silica as existing in plants is united with 

 potash and soda, and may be said to be insoluble 

 in water ; but by the fermentation and decay of 

 these plants carbonic acid is liberated, which 

 uniting with the potash and soda forms car- 

 bonates of these substances, and the silica is 

 separated as hydrated or soluble silica, to supply 

 the wants of growing plants. 



In the production of wheat and other cereals, 

 the presence of this element, in a soluble state, is 

 of the first importance in building up the straw 

 or stalk. 



If the reader refers to the tables showing the 

 composition of the straw of the different grain 

 crops, he will see what a large amount of this 

 substance is required. 



As the amount of soluble silica in the most 

 of soils is comparatively small, every fanner 

 who wishes to raise wheat or other grain, will 

 see the importance of returning every particle 

 of straw to his land to furnish this substance. 



Another source of soluble silica at the com- 

 mand of the farmer are the weeds and iwds 

 that grow in swampy places or running water, 



