e 30 feet deep.--Mechi's Parsnips 13 feet
long!--Drainage promotes Pulverization.--Prevents
Surface-Washing.--Lengthens the Season.--Prevents Freezing
out.--Dispenses with Open Ditches.--Saves 25 per cent. of
Labor.--Promotes absorption of Fertilizing Substances from the
Air.--Supplies Air to the Roots.--Drains run before Rain; so do
some Springs.--Drainage warms the Soil.--Corn sprouts at 55 deg.; Rye
on Ice.--Cold from Evaporation.--Heat will not pass downward in
Water.--Count Rumford's Experiments with Hot Water on
Ice.--Aeration of Soil by Drains.

The benefits which high-lands, as we ordinarily call them, in
distinction from swamp or flowed lands, derive from drainage, may be
arranged in two classes, _mechanical_ and _chemical_; though it is not
easy, nor, indeed, is it important, to maintain this distinction in all
points. Among those which partake rather of the nature of mechanical
changes, are the following:

_Drainage deepens the soil._ Every one who has attempted to raise
deep-rooted vegetables upon half-drained swamp-land, has observed the
utter impossibility of inducing them to extend downward their usual
length. Parsnips and carrots, on such land, frequently grow large at the
top, but divide into numerous small fibres just below the surface, and
spread in all directions. No root, except those of aquatic plants, will
grow in stagnant water. If, therefore, it is of any advantage to have a
deep, rather than a shallow soil, it is manifestly necessary, from this
consideration alone, to lower the line of standing water, at least, to
the extent to which the roots of our cultivated crops descend. A deep
soil is better than a shallow one, because it furnishes a more extensive
feeding-ground for the roots. The elements of nutrition, which the plant
finds in the soil, are not all upon the surface. Many of them are washed
down by the rains into the subsoil, and some are found in the
decomposing rocks themselves. These, the plants, by a sort of instinct,
search out and find, as well in the depths of the earth as at its
surface, if no obstacle opposes. By striking deep roots again, the
plants stand more firmly in the earth, so that they are not so readily
drawn out, or shaken by the winds. Indeed, every one knows that a soil
two feet deep is better than one a foot deep; and market-gardeners and
nursery-men show, by their practice, that they know, if others do not,
that a t