THE PLANT. 29 



3. It is a strong agent in the decomposition of vege- 

 table matter, and is thus of much importance in pre- 

 paring manures. 



4. It roughens the smooth round particles of sandy 

 soils, and prevents their compacting, as they are 

 often liable to do. 



5. It is also of use in killing certain kinds of insects, 

 and, when externally applied, in smoothing the bark 

 of fruit trees. 



The source from which this and the other earthy 

 matters required are to be obtained, will be more 

 fully considered in the section on manures. 



SODA. 



Soda, one of the alkalies contained in the ashes 

 of plants, is very much the same as potash in its agri- 

 cultural character and uses. Soda exists very largely 

 in nature, as it forms an important part of common 

 salt, whether in the ocean or in those inland deposits 

 known as rock salt. When combined with sulphuric 

 acid it forms sulphate of soda or Glauber's salts. 

 In combination with carbonic acid, as carbonate of 

 soda, it forms the common washing soda of the shops. 



LIME. 



Lime is in many ways important in agriculture : 



1. It is a constituent of plants and animals. 



2. It assists in the decomposition of vegetable 

 matter in the soil as well as of its minerals. 



3. It corrects the acidity* of sour soils. 



* Sourness. 



