

IN THE SOIL AND IN THE PLANT. 189 



The latter salt will then act in one or other of the ways above 

 described. 



c Sulphate and phosphate of ammonia will, in like manner,,, 

 yield their acid more or less completely to potash, to soda, to lime, 

 and perhaps to magnesia, forming sulphates and phosphates of 

 these substances, while their ammonia is converted into carbonate. 



d Nitrate of ammonia will give up a part of its acid to any 

 earthy or alkaline carbonates which may exist in the soil, and 

 will be thus partly converted into carbonate. Its acid may also 

 contribute, by the oxygen it contains, to promote the decom- 

 position of organic matter ; but this will only take place beneath 

 the surface, where the light does not penetrate, and where much 

 organic matter is present. 



Nitrate of ammonia exists in and is naturally formed in most 

 soils. It yields its nitric acid to the carbonates of lime and 

 magnesia when they are present in the soil, and is itself con- 

 verted into carbonate. Thus, while it brings the lime and 

 magnesia into a state in which they can readily enter the plant, 

 the ammonia becomes itself capable of decomposing sulphates 

 and chlorides, either in the soil or in the plant. 



e The acetate, oxalate, and humate of ammonia, may all 

 undergo slow oxidation in the surface soil, producing nitric acid 

 from the ammonia, and carbonic acid from the acetic, oxalic, 

 and humic acids which they contain. 



2. Functions in the plant. The salts of ammonia may un- 

 dergo the above changes more or less completely in the soil, 

 but they may also enter directly into the roots of plants, and 

 perform certain functions which are important to their healthy 

 and rapid growth. Thus, 



a They supply nitrogen an element very necessary to the 

 growing plant in a form in which it is immediately available 

 for the production of those nitrogenous compounds which not 

 only form an important part of the substance of the plant, but 

 appear also to preside over those chemical changes constantly 

 taking place in its sap, and upon which the health and rapidity 

 of its growth depend. 



These substances protein compounds they are called exist 

 in large proportion in the extremities of the roots, and are 



