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We may hence deduce three important practical re- 
marks : — 
1. That the dung of cattle is much inferior to the animal 
liquid excretions. 
2. That the liquid manures should not be exposed to the 
atmosphere prior to their use, as the volatile ammonia quickly 
evaporates. 
3. That the Cerealia, as Wheat, Barley, Oats, which con- 
tain the greatest quantity of nitrogen, should have applied to 
them the liquid animal manures. 
III. Phosphates and Neutral Salts. 
Carbonic acid, water and ammonia, are necessary for the 
existence of plants, because they contain the elements from 
which all their organs are formed ; they are strictly the 
pabulum vitae. But there are other substances obtained from 
the inorganic kingdom, which are necessary for particular 
parts of plants. Such inorganic constituents exist in small 
quantities in those parts of a plant in which the process of 
assimilation is most active, as in the mass of woody fibre, and 
the leaves contain more inorganic matter than the branches, 
and the branches more than the stem. The potatoe plant 
contains more potash before blossoming than after it. These 
substances are found in the ashes after incineration. 
" Most plants, (says Liebig,) perhaps all of them, contain 
organic acids, all of which are in combination with bases such 
as potash, soda, lime, or magnesia. These bases evidently regu- 
late the formation of the acids, for the diminution of the one 
is followed by a decrease of the other, e. g. the quantity of 
potash contained in the juice of grapes is less, when it is ripe 
than when unripe, and it is certain that these substances ex- 
ercise an important influence on the development of seeds. 
Again, he says, that any one of the alkaline bases may be 
substituted for another, the action of all being the same; but 
