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condition in which they are present. A soil however, which
would contain no other substances but pure sand, clay, peroxyd
of iron, lime and humus, and even these in such a proportion as
is considered the most proper, would be in spite of the highest cul-
ture entirely sterile. In the following section we shall become ac-
quainted with a series of substances which are essential to vegeta-
ble life, inasmuch as they are required by plants as nourishment;
and as they can be supplied by no other means than by the soil
itself, they must be present in it whenever the soil exercises fer-
tilizing properties. This series of substances includes all those in
soils which by their chemical character belong to the class of salts,
and which are more or less soluble in rain water, and by means of
their solution therefore capable of entering into the organization of
plants; the fundamental ingredients of soil show in every respect
quite a different character, as already stated. These salts consist
principally of the following: alkaline salts, (potash and soda,)
earthy salts, (lime and magnesia,) phosphates, (salts of phosphoric
acid,) sulphates, (salts of sulphuric acid,) chlorides, (salts of hy-
drochloric acid,) and silicates, (salts of silicic acid.)

Total sterility of a soil, as we supposed it in the foregoing, rare-
ly exists in reality, inasmuch as the absolute absence of soluble
substances, can only be in a field which would entirely consist of
fine quartz sand; the presence of clay and humus, includes at the
same time that of alkaline salts, some of which are always retain-
ed by them, so that, a chemically pure clay and a chemically pure
humus, never exist in soils. The former will never become totally
decomposed, and the latter will always retain some of these substan-
ces as long as it is present itself, and not totally transformed into
carbonic acid and water. It may happen that a soil, which con-
sists of the fundamental ingredients and from which a series of
crops were taken, does show only traces of those nourishing sub-
stances, or even none at all, when they are to be extracted by water;
but this state does not indicate that of absolute sterility, but merely
that of temporary sterility, inasmuch as it yet contains nourish-
ing substances, which, however, are retained by clay and humus
in such a form that water may not extract them. After several fal-
lowing-seasons, by exposure to the air, which may be increased
by mechanical loosening of the earth, by deepening of the soil,
&c., the fertility of the soil may be restored, in consequence of
the advanced disintegration of clay and humus, by which new
quantities of soluble substances become liberated.

We have in the foregoing considered the important part which
the fundamental ingredients of soil take in the development of
plants, inasmuch as it depends on their relative proportion and on
the condition in which they are present, as a soil is more or less
fit to offer those supports which vegetable life requires. In the
following I shall endeavor to explain, how the quantity of solu-