often as many as 38,200 on a single square inch. Fig. 17 shows how a
root looks when it has been cut crosswise into what is known as a cross
section. The figure is much increased in size. You can see how the
root-hairs extend from the root in every direction. Fig. 18 shows a
single root-hair very greatly enlarged, with particles of sand sticking
to it.

[Illustration: FIG. 17. A SLICE OF A ROOT
Highly magnified]

These hairs are the feeding-organs of the roots, and they are formed
only near the tips of the finest roots. You see that the large, coarse
roots that you are familiar with have nothing to do with _absorbing_
plant food from the soil. They serve merely to _conduct_ the sap and
nourishment from the root-hairs to the tree.

When you apply manure or other fertilizer to a tree, remember that it is
far better to supply the fertilizer to the roots that are at some
distance from the trunk, for such roots are the real feeders. The plant
food in the manure soaks into the soil and immediately reaches the
root-hairs. You can understand this better by studying the distribution
of the roots of an orchard tree, shown in Fig. 19. There you can see
that the fine tips are found at a long distance from the main trunk.

[Illustration: FIG. 18. A ROOT-HAIR WITH PARTICLES OF SOIL STICKING
TO IT]

You can now readily see why it is that plants usually wilt when they are
transplanted. The fine, delicate root-hairs are then broken off, and the
plant can but poorly keep up its food and water supply until new hairs
have been formed. While these are forming, water has been evaporating
from the leaves, and consequently the plant does not get enough moisture
and therefore droops.

[Illustration: FIG. 19. DISTRIBUTION OF APPLE-TREE ROOTS]

Would you not conclude that it is very poor farming to till deeply any
crop after the roots have extended between the rows far enough to be cut
by the plow or cultivator? In cultivating between corn rows, for
example, if you find that you are disturbing fine roots, you may be sure
that you are breaking off millions of root-hairs from each plant and
hence are doing harm rather than good. Fig. 20 shows how the roots from
one corn row intertangle with those of another. You see at a glance how
many of these roots would be destroyed by deep cultivation. Stirring
the upper inch of soil when the plants are well grown is sufficient
tillage and does no injury to the roots.

[Illustration: FIG. 20. CORN R