AMERICAN INSTITUTE. 163 



for new weeds, and for the growth of wild parsnips, of jolinswort, and other 

 similar pests, which appear ; when by cultivation of the soil, the oxygen 

 is permitted to reach the seeds, and they vivify them into life. Silicates 

 insoluble in water are found by analysis in the leaves and stems of almost 

 all plants. How do they get there? They are decomposed in the soil by 

 the action of carbonic acid gas, which abstracts the potash from the silica, 

 and forms carbonates of its base. These are carried down to enrich the 

 soil by rain. Carbonic acid likewise decomposes felspar, the silicates of 

 hornebiende, and granitic rocks, all of which it converts into soil. 



Having considered the mechanical constitution, and origin of soils, 

 I will now take up the other portion of my subject, the chemical con- 

 stitution of soils. They must perform four separate functions in reference 

 to the growth of plants. 



1. It must hold up and sustain the growing plant, by affording it a sure 

 and strong position. 



2. It must advance its growth towards maturity, by absorbing heat, air, 

 and water for it. 



3. It must keep the plant at all times thoroughly supplied with inor- 

 ganic and organic food. 



4. It must cause chemical changes to be constantly carried on, so as to 

 prepare food requisite to be admitted into the roots of plants, and it is the 

 business of the agriculturist so to improve the soil as to aid nature in the 

 performance of these great works. And we must chemically improve our 

 soils on the following principles. 



1. That it must have in it a certain amount of organic food, and a vari- 

 able quantity of nitrogen. 



2. That inorganic food in many varieties must be contained in it. 



3. That notwithstanding the different plants usually cultivated require 

 different varieties of inorganic food, still, if it is in the ground, they will 

 take it up in different proportions, and thus satisfy themselves. 



4. That of one soil contains a large proportion of inorganic food, and 

 another is deficient, we can meet the difficulty, by planting those seeds 

 which require a large quantity in one, and those more easily satibfied with 

 a small quantity in the other. 



On the principles above named, hang the entire art of improving the 

 soil chemically. 



We have now reached a point that will enable me to take up and con- 

 sider the mineral manures, saline and earthy. Among the saline may be 

 named : 



1. Carbonate of potash, which may be obtained in the crude form, or in 

 the shape of pearlash, but at too high a price to use extensively for the 

 cultivation of crops. 



r 2. Carbonate of soda. This may be bought at a price that will enable 

 all to use it to great advantage on grass lands, particularly if overrun with 

 a mossy growth, or abounding in the poisonous sulphate of iron. It is 

 applied advantageously in weak solution, by water-cart, or horse. I have 



