ating through the cooler soil.

When rain falls on the parched surface soil, it robs it of a portion of
its heat, which is carried down to equalize the temperature for the
whole depth. The heat of the rain-water itself is given up to the soil,
leaving the water from one to ten degrees cooler, when it passes out of
the drains, than when received by the earth.

There is always a current of air passing from the lower to the upper end
of a well constructed drain; and this air is always cooler in warm
weather, when it issues from, than when it enters the drain. Its lost
heat is imparted to the soil.

[How does it hasten the decomposition of roots and other
organic matter in the soil?

How does it accelerate the disintegration of its mineral parts?

Why is this disintegration necessary to fertility?]

This heating of the lower soil renders it more favorable to vegetation,
partially by expanding the spongioles at the end of the roots, thus
enabling them to absorb larger quantities of nutritious matters.

4. Under-draining _hastens the decomposition of roots and other organic
matters in the soil_, by admitting increased quantities of air, thus
supplying _oxygen_, which is as essential in decay as it is in
combustion. It also allows the resultant gases of decomposition to pass
away, leaving the air around the decaying substances in a condition to
continue the process.

This organic decay, besides its other benefits, produces an amount of
heat perfectly perceptible to the smaller roots of plants, though not so
to us.

5. Draining _accelerates the disintegration of the mineral matters in
the soil_, by admitting water and oxygen to keep up the process. This
disintegration is necessary to fertility, because the roots of plants
can feed only on matters dissolved from _surfaces_; and the more finely
we pulverize the soil, the more surface we expose. For instance, the
interior of a stone can furnish no food for plants; while, if it were
finely crushed, it might make a fertile soil.

Any thing, tending to open the soil to exposure, facilitates the
disintegration of its particles, and thereby increases its fertility.

[How does under-draining equalize the distribution of the
fertilizing parts of the soil?

Why does this distribution lessen the impoverishment of the soil?

How does under-draining improve the mechanical texture of the soil?

How do drains affect the excrementitious matter of plants?]

6. Draining _causes