nd under all circumstances, but
the more nearly it is maintained, the more nearly perfect will be the
results of cultivation.

*Chemical Action in the Soil.*--Plants receive certain of their
constituents from the soil, through their roots. The raw materials from
which these constituents are obtained are the minerals of the soil, the
manures which are artificially applied, water, and certain substances
which are taken from the air by the absorptive action of the soil, or are
brought to it by rains, or by water flowing over the surface from other
land.

The mineral matters, which constitute the ashes of plants, when burned,
are not mere accidental impurities which happen to be carried into their
roots in solution in the water which supplies the sap, although they vary
in character and proportion with each change in the mineral composition of
the soil. It is proven by chemical analysis, that the composition of the
ashes, not only of different species of plants, but of different parts of
the same plant, have distinctive characters,--some being rich in
phosphates, and others in silex; some in potash, and others in lime,--and
that these characters are in a measure the same, in the same plants or
parts of plants, without especial reference to the soil on which they
grow. The minerals which form the ashes of plants, constitute but a very
small part of the soil, and they are very sparsely distributed throughout
the mass; existing in the interior of its particles, as well as upon their
surfaces. As roots cannot penetrate to the interior of pebbles and compact
particles of earth, in search of the food which they require, but can only
take that which is exposed on their surfaces, and, as the oxydizing effect
of atmospheric air is useful in preparing the crude minerals for
assimilation, as well as in decomposing the particles in which they are
bound up,--a process which is allied to the _rusting_ of metals,--the more
freely atmospheric air is allowed, or induced, to circulate among the
inner portions of the soil, the more readily are its fertilizing parts
made available for the use of roots. By no other process, is air made to
enter so deeply, nor to circulate so readily in the soil, as by
under-draining, and the deep cultivation which under-draining facilitates.

Of the manures which are applied to the land, those of a mineral character
are affected by draining, in the same manner as the minerals which are
native to the soil; whi