will be the crop which grows above the soil.

Of what value is it to the farmer to know that the roots of farm
plants penetrate to depths of five or six feet in the soil? To answer
this question it will be necessary for us to know something of the
conditions necessary for root growth. So we will leave this till
later.

Of what value is it to the farmer to know that many of the roots of
his farm plants come very near the surface of the soil? It tells him
that he should be careful in cultivating his crop to injure as few of
these roots as possible. In some parts of the country, particularly in
the South, the tool commonly used for field cultivation is a small
plow. This is run alongside of the row, throwing the soil from the
crop, and then again throwing the soil to the crop. Suppose we
investigate, and see how this affects the roots of the crop.

[Illustration: FIG. 8.
Sweet potato roots. The great mass of the roots is in the plowed soil.
Many of them reach out 5 to 7 feet from the plant. Some reach a depth
of more than 5 feet, and others come to the very surface of the soil.]

[Illustration: FIG. 9.
Soy-bean roots showing location, extent and depth of root-growth.]

Let us visit a field where some farmer is working a crop with a plow,
or get him to do it, for the sake of the lesson. We will ask him to
stop the plow somewhere opposite a plant, then we will dig a hole a
little to one side of the plow and wash away the soil from over the
plow (see Fig. 10), and see where the roots are. We will find that the