ogen which they
contain usually unites with hydrogen, and forms ammonia. In consequence
of this the atmosphere always contains more or less of this gas, arising
from the decay, etc., which is continually going on all over the world.

This ammonia in the atmosphere is the capital stock to which all plants,
not artificially manured, must look for their supply of nitrogen. As
they can take up ammonia only through their roots, we must discover
some means by which it may be conveyed from the atmosphere to the soil.

[Does water absorb it?

What is _spirits of hartshorn_?

Why is this power of water important in agriculture?

What instance may be cited to prove this?]

Water may be made to absorb many times its bulk of this gas, and water
with which it comes in contact will immediately take it up. Spirits of
hartshorn is merely water through which ammonia has been passed until it
is saturated.[A] This power of water has a direct application to
agriculture, because the water constituting rains, dews, &c., absorbs
the ammonia which the decomposition of nitrogenous matter had sent into
the atmosphere, and we find that all rain, snow and dew, contain
ammonia. This fact may be chemically proved in various ways, and is
perceptible in the common operations of nature. Every person must have
noticed that when a summer's shower falls on the plants in a flower
garden, they commence their growth with fresh vigor while the blossoms
become larger and more richly colored. This effect cannot be produced by
watering with spring water, unless it be previously mixed with ammonia,
in which case the result will be the same.

Although ammonia is a gas and pervades the atmosphere, few, if any,
plants can take it up, as they do carbonic acid, through their leaves.
It must all enter through the roots in solution in the water which goes
to form the sap. Although the amount received from the atmosphere is of
great importance, there are few cases where artificial applications are
not beneficial. The value of farm-yard and other animal manures, depends
chiefly on the ammonia which they yield on decomposition. This subject,
also the means for retaining in the soil the ammoniacal parts of
fertilizing matters, will be fully considered in the section on manures.

[Can plants use more ammonia than is received from the
atmosphere?

On what does the value of animal manure chiefly depend?

What changes take place after ammonia enters the plant?

May