of these very substances in the body of the soil itself, and
which also exercises an attractive power for these nutriments,
and retains and reserves them if they have once become ap-
propriated by the soil.

Among them, water is the most common and abundant, for
the supply of which nature provides in a liberal manner.
But in spite of its being met with almost every where in na-
ture, we are well aware of the fact that it is not seldom want-
ed, and then usually at a time when the plants need it most
urgently for their final development. The injurious effect of
dry seasons on present crops is well known. On the other
hand we meet soils entirely destitute of productiveness, and
find, upon examination, that their sterility is the consequence
of their wet condition, they being saturated with moisture,
and even permit the water to rest upon them and to remain
there for a considerable length of time. If by some means
the water is removed from this kind of soils, they are at once
rendered fertile and fit to reach the highest state of culture.

This state of things shows clearly that the water, though
a nutriment to plants that cannot be dispensed with, is never-
theless, to the highest extent injurious to vegetation, if per-
mitted to accumulate in the soil; and as the condition of the
Boil, as a body at large, is due to its mechanical texture, or
to the proportion in which the fundamental constituents are
present in it, it follows that a regular supply of this nutri-
ment, neither more nor less than wanted, can only be secured
by a proper mechanical texture of the soil. In this case the
soil will, at one time, reserve to the utmost, the needed quan-
tity of water, whilst at another, it will freely dispense with
all superabundance.

The quantity of water required by plants during their
growth is very considerable. It is the medium by which all
other nutriments are conveyed to the plants, and with which
they dispense again as soon as this function has been fulfilled.
Boussingault states that annually by a good crop from one
acre, about six millions pounds of water evaporated from the
leaves of the plants that was previously taken up by their
roots. Besides, plants contain about 12 per cent, of their
weight of water in the dry state, which forms a constituent
part of their body.

Carbonic acid, the second of this class of nutriments, is the
substance from which plants derive all their carbon, or about
43 per cent, of their whole weight. A regular supply of car-
bonic acid is likewise dependent on the mechanical texture
of the soil; for carbonic acid is the product of the decomposi-
tion of humus, a substance which forms a fundamental con-

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