the ground. Under the plank the soil is wet, while the soil not covered
by the plank is dry. Why? Capillarity brought the water to the surface,
and the plank, by keeping away wind and warmth, acted as a trap to hold
the moisture. Now of course a farmer cannot set a trap of planks over
his fields, but he can make a trap of dry earth, and that will do just
as well.

When a crop like corn or cotton or potatoes is cultivated, the fine,
loose dirt stirred by the cultivating-plow will make a mulch that serves
to keep water in the soil in the same way that the plank kept moisture
under it. The mulch also helps to absorb the rains and prevents the
water from running off the surface. Frequent cultivation, then, is one
of the best possible ways of saving moisture. Hence the farmer who most
frequently stirs his soil in the growing season, and especially in
seasons of drought, reaps, other things being equal, a more abundant
harvest than if tillage were neglected.

=EXERCISE=

1. Why is the soil wet under a board or under straw?

2. Will a soil that is fine and compact produce better crops than
one that is loose and cloddy? Why?

3. Since the water which a plant uses comes through the roots, can
the morning dew afford any assistance?

4. Why are weeds objectionable in a growing crop?

5. Why does the farmer cultivate growing corn and cotton?

SECTION IV. HOW THE WATER RISES IN THE SOIL

[Illustration: FIG. 8. USING LAMP-CHIMNEYS TO SHOW THE RISE OF WATER
IN SOIL]

When the hot, dry days of summer come, the soil depends upon the
subsoil, or undersoil, for the moisture that it must furnish its growing
plants. The water was stored in the soil during the fall, winter, and
spring months when there was plenty of rain. If you dig down into the
soil when everything is dry and hot, you will soon reach a cool, moist
undersoil. The moisture increases as you dig deeper into the soil.

Now the roots of plants go down into the soil for this moisture, because
they need the water to carry the plant food up into the stems and
leaves.

You can see how the water rises in the soil by performing a simple
experiment.

=EXPERIMENT=

Take a lamp-chimney and fill it with fine, dry dirt. The dirt from
a road or a field will do. Tie over the smaller end of the
lamp-chimney a piece of cloth or a pocket handkerchief, and place
this end in a shallow pan of water. If the s