effect we can close the pores somewhat by compacting the
soil with the roller. For more lasting effects, we can fill them with
organic matter.

Which soils will hold longest the water which they have absorbed? Or
which soils will keep moist longest in dry weather?

[Illustration: FIG. 23.
To show how bottles may be used in place of lamp chimneys shown in
Figs 22 and 24.]

[Illustration: FIG. 24.--CAPILLARITY OF SOILS
To show the relative powers of soils to take water from below.]

[Illustration: FIG. 25.--WATER-ABSORBING AND WATER-HOLDING POWERS OF
SOILS.]

=Experiment.=--Fill a pan or bucket with moist sand, another with
moist clay, and a third with moist organic matter; set them in the sun
to dry and notice which dries last. The organic matter will be found
to hold moisture much longer than the other soils. The power of the
other soils to hold moisture through dry weather can be improved by
mixing organic matter with them.

We find then that the power of soils to absorb and hold moisture
depends on the amount of sand, clay, or humus which they contain, and
the compactness of the particles. We see also how useful organic
matter is in improving sandy and clayey soils.

THE EFFECT OF WORKING SOILS WHEN WET

By this time the soils we left in the pans (see page 26), sand, clay,
humus and garden soil, must be dry. If so, examine them. We find that
the clay which was stirred when wet has dried into an almost bricklike
mass, while that which was not stirred is not so hard, though it has a
thick, hard crust. The sand is not much affected by stirring when wet.
The organic matter which was stirred when wet has perhaps stiffened a
little, but very easily crumbles; the unstirred part was not much
affected by the wetting and drying.

The garden soil after drying is not as stiff as the clay nor as loose
as the sand and humus. This is because it is very likely a mixture of
all three, the sand and the humus checking the baking. This teaches
us that it is not a good plan to work soils when they are wet if they
are stiff and sticky; and that our stiff clay soils can be kept from
drying hard or baking by the use of organic matter. "And that's a
witness" for organic matter.

The relation of the soil to moisture is very important, for moisture
is one of the greatest factors if not the greatest in the growth of
the crop.

The power to absorb or soak up moisture from any source is greatest in
those soils whose particles are