process of decomposition; the latter being more fixed and not sus-
ceptible of change by causes which entirely destroy the combina-
tions of the former. Let a piece of wood or straw, grains of
wheat, or any other vegetable substances be exposed to a red heat,
with free access of air, and we find, after a certain time, that their
forms are changed, their bulk very much diminished, and a large
proportion of their weight dissipated, there being left behind only
a small quantity of what are commonly called ashes. These are
the inorganic, or mineral, whilst the parts which have disappeared
are the organic constituents of vegetable structure.

The part which has disappeared in the air is that portion of
plants which was almost entirely obtained from the air during their
growth, the part remaining and called the ashes, that which com-
poses the inorganic or mineral part, is that portion furnished en-
tirely by the soil, because it does not and cannot exist in the air.
The part which is dissipated by heat, called organic or vegeta-
ble matter, forms by far the largest proportion of the weight and
bulk of all vegetable and animal structures, composing generally
from ninety to ninety-eight per cent, of their weight. Although
the elements of organic matter form so large a proportion of all
living bodies, yet they are not more essential to their existence than
the inorganic or mineral portion.

The elements or constituent parts of organic matter are Carbon,
Oxygen, Hydrogen, and Nitrogen, which, by their combinations
with each other, form by far the largest part of the weight of all
living bodies. Some of these elements, moreover, constitute the
water which is found in the earth, the matter of the atmosphere
which we breathe, and also in combination with mineral matter a
very large proportion of the solid parts of the earth. Bodies ex-
isting so abundantly, so widely disseminated throughout the uni-
verse, are most important subjects for consideration and for atten-
tive study. They are things which must be known, before suc-
cessful agriculture can be practiced.

ORGANIC ELEMENTS.

Carbon and Carbonic Acid.—Of all the constituents of vege-
table life, carbon is the most abundant. In its pure state it exists
as a solid, differing in this respect from the other three, which
naturally exist in an aeriform or gaseous state. It is the essential
principle of the different varieties of charcoal. It is the chief
constituent of all of those immense beds of bituminous and anthra-
cite coal found in various parts of the earth. It is abundantly
formed by burning wood, with but slight access of air, and can
also be produced in a very pure form from sugar, turpentine, starch

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