sort of "parrot" instruction in
almost baby language instead of established facts and principles in
definite and permanent scientific terms. The farmer should be as
familiar with the names of the ten essential elements of plant food
as he is with the names of his ten nearest neighbors. Safe and
permanent systems of soil improvement and preservation may come with
intelligence--never with ignorance--on the part of the landowners.

When the knowledge becomes general that food for plants is just as
necessary as food for animals, then American agriculture will mean
more than merely working the land for all that's in it. This
knowledge is as well established as the fact that the earth is
round, although the people are relatively few who understand or make
intelligent application of the existing information.

Agricultural plants consist of ten elements, known as the essential
elements of plant food; and not a kernel of corn or a grain of
wheat, not a leaf of clover or a spear of grass can be produced if
the plant fails to secure any one of these ten elements. Some of
these are supplied to plants in abundance by natural processes;
others are not so provided and must be supplied by the farmer, or
his land becomes impoverished and unproductive.

Foods That Plants Live On

Two elements, carbon and oxygen, are contained in normal air in the
form of a gas called carbon dioxid, and this compound is taken into
the plant through the breathing pores, which are microscopic
openings located chiefly on the under side of the leaves. Some
plants have more than a hundred thousand breathing pores to the
square inch of leaf surface.

When plants or plant products are burned or decomposed the carbon of
the combustible material--grass, wood, coal, and so forth--unites
with the free oxygen of the atmosphere to re-form the carbon dioxid,
which thus returns as a gas to the air. Even the food taken into the
animal system, after being digested and carried into the blood, is
brought, into contact with the oxygen of the air--which also passes
into the blood through the cell walls of the lungs--and a form of
combustion takes place, the heat generated serving to warm the body
while the carbon dioxid passes back into the lungs and is exhaled
into the open air.

By these circulation processes the supply of carbon dioxid in the
atmosphere is renewed and maintained without any special effort on
the part of man. Hydrogen is one of the elements of wh