n to be most injurious
to vegetation.

The removal of water from the lower part of the soil, and the admission
of air, which is the consequence of draining, submits that part of it to
the same changes which take place in its upper portion, and has the
effect of practically deepening the soil to the extent to which it is
thus laid dry. The roots of the plants growing on the soil, which stop
as soon as they reach the moist part, now descend to a lower level, and
derive from that part of it supplies of nourishment formerly
unavailable. The deepening of the soil has further the effect of making
the plants which grow upon it less liable to be burned up in seasons of
drought, a somewhat unexpected result of making a soil drier, but which
manifestly depends on its permitting the roots to penetrate to a greater
depth, and so to get beyond the surface portion, which is rapidly dried
up, and to which they were formerly confined.

It may be added also that the abundant escape of water from the drains
acts chemically by removing any noxious matters the soil may contain,
and by diminishing the amount of soluble saline matters, which sometimes
produce injurious effects. It thus prevents the saline incrustation
frequently seen in dry seasons on soils which are naturally wet, and
which is produced by the water rising to the surface by capillary
attraction, and, as it evaporates, depositing the soluble substances it
contained, as a hard crust which prevents the access of air to the
interior of the soil.

It is thus obvious that the drainage of the soil modifies its properties
both mechanically and chemically. It exerts also various other actions
in particular cases which we cannot here stop to particularize. It
ameliorates the climate of districts in which it is extensively carried
out, and even affects the health of the population in a favourable
manner. The sum of its effects must necessarily differ greatly in
different soils, and in different districts; but a competent
authority[J] has estimated, that, on the average, land which has been
drained produces a quarter more grain per acre than that which is
undrained. But this by no means exhausts the benefits derived from it,
draining being merely the precursor of further improvement. It is only
after it has been carried out that the farmer derives the full benefit
of the manures which he applies. He gains also by the increased facility
of working the soil, and by the rapidity with wh