MANURES . 



31 



mixed ; into nitrogenous, carbonaceous, earthy, and saline ; 

 and into general and special. Organic manures include 

 those both of animal and vegetable origin ; inorganic ma- 

 nures are derived from minerals. 



Manures may have a two-fold action — directly assisting 

 vegetable growth by entering into the composition of 

 plants, and by supplying them with moisture and nutri- 

 tive gases which they absorb from the atmosphere. Ma- 

 nures may also indirectly assist the growth of plants 

 •either by destroying vermin or weeds ; by decomposing in 

 the soil, and rendering available any stubborn organic re- 

 mains therein ; by protecting plants from sudden changes 

 of temperature ; or they may act as amendments by im- 

 proving the texture and physical condition of the soil. 

 All the above properties probably never are combined in 

 any one manure, each being characterized by superiority 

 in some one of the above qualities. 



The manures most generally applicable are those com- 

 posed of substances which directly enter into and are es- 

 sential to the growth of plants. What are these sub- 

 stances ? 



" Plants," says Liebig, " contain combustible and in- 

 combustible ingredients. The latter, which compose the 

 ash left by all parts of plants on combustion, consist, in 

 the case of our cultivated plants, essentially of phosphoric 

 acid, potash, silicic and sulphuric acids, iime, iron, mag- 

 nesia, and chloride of sodium." It is now fully establish- 

 ed " that the constituents of the ash are elements of food, 

 and hence indispensable to the structure of the different 

 parts of the plant." 



The few ashes that remain after burning a plant are all 

 that it got necessarily from the soil. From eighty-eight 

 to ninety-nine per cent of the weight of the plant has es- 

 caped into the air, from which, and from water, the plant 

 has derived it immediately or remotely. The composition 

 of their ashes varies in different parts of the same plant 



