t a point at which
they can be made use of by the roots of plants.

2. Charcoal in the soil causes it to appropriate larger quantities of
the fertilizing gases of the atmosphere, on account of its power, as
just named, to absorb gases.

The atmosphere contains results, which have been produced by the
breathing of animals and by the decomposition of various kinds of
organic matter, which are exposed to atmospheric influences. These gases
are chiefly ammonia and carbonic acid, both of which are largely
absorbed by water, and consequently are contained in rain, snow, etc.,
which, as they enter the soil, give up these gases to the charcoal, and
they there remain until required by plants. Even the air itself, in
circulating through the soil, gives up fertilizing gases to the carbon,
which it may contain.

3. Charcoal gives to the soil power to absorb moisture, because it is
itself one of the best absorbents in nature; and it has been proved by
accurate experiment that peaty soils absorb moisture with greater
rapidity, and part with it more slowly than any other kind.

[How does it render it warmer?

Is the heat produced by the decomposition of organic matter perceptible
to our senses?

Is it so to the growing plant?

What is another important part of the organic matter in the soil?]

4. Carbon in the soil renders it warmer, because it darkens its color.
Black surfaces absorb more heat than light ones, and a black coat, when
worn in the sun, is warmer than one of a lighter color. By mixing carbon
with the soil, we darken its color, and render it capable of absorbing a
greater amount of heat from the sun's rays.

It will be recollected that, when vegetable matter decomposes in the
soil, it produces certain gases (carbonic acid, etc.), which either
escape into the atmosphere, or are retained in the soil for the use of
plants. The production of these gases is always accompanied by _heat_,
which, though scarcely perceptible to our senses, is perfectly so to the
growing plant, and is of much practical importance. This will be
examined more fully in speaking of manures.

[How is it obtained by the soil?

What offices does the organic matter in the soil perform?]

Another important part of the organic matter in the soil is that which
contains _nitrogen_. This forms but a very small portion of the soil,
but it is of the greatest importance to vegetables. As the nitrogen in
food is of absolute necessity to the growth of