THE PHILOSOPHY OF FARMING. 589 
remains then in the soil, and acted upon by the 
aeration of the soil, and are thereby speedily 
reduced to their primordial elements ; and these 
elements being in immediate contact with the 
roots of plants, are immediately absorbed into 
the plants, and carried like stones, ready hewn, 
when one structure is pulled down to build up 
another, to construct the solid portions of the 
living fabrick. Nor is it that aeration of soils is 
thus serviceable in promoting the decay of organ- 
ised matter in soils; but it likewise slowly acts in 
the reduction of mineral matter, so as to render 
it soluble in the moisture of the soil, that it also 
may thence be carried into such vegetable systems 
as require it, so that aeration accomplishes every 
thing which plants may want in the medium of the 
soil for growth and sustenance. 
But this action of aeration within soils must 
soon expend the organised and mineral stores 
within the sphere of its action. Plants, therefore, 
which grew and prospered most luxuriantly upon 
its first introduction, must by and by begin to 
languish as they reduce their supplies. When 
nature has thus exhausted her means by her own 
energies, then art comes forward to her assistance. 
The produce of the field being carried off, or 
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