about one-fifth of the
rain-fall. Water thus deposited on the soil is absorbed more or less
completely, in proportion to the porosity of the ground.

The extent to which plants will be affected by drought depends, other
things being equal, on the depth to which they send their roots. If these
lie near the surface, they will be parched by the heat of the sun. If they
strike deeply into the damper subsoil, the sun will have less effect on
the source from which they obtain their moisture. Nothing tends so much to
deep rooting, as the thorough draining of the soil. If the _free_ water be
withdrawn to a considerable distance from the surface, plants,--even
without the valuable aid of deep and subsoil plowing,--will send their
roots to great depths. Writers on this subject cite many instances in
which the roots of ordinary crops "not mere hairs, but strong fibres, as
large as pack-thread," sink to the depth of 4, 6, and in some instances 12
or 14 feet. Certain it is that, in a healthy, well aerated soil, any of
the plants ordinarily cultivated in the garden or field will send their
roots far below the parched surface soil; but if the subsoil is wet, cold,
and soggy, at the time when the young crop is laying out its plan of
future action, it will perforce accommodate its roots to the limited space
which the comparatively dry surface soil affords.

It is well known among those who attend the meetings of the Farmers' Club
of the American Institute, in New York, that the farm of Professor Mapes,
near Newark, N.J., which maintains its wonderful fertility, year after
year, without reference to wet or dry weather, has been rendered almost
absolutely indifferent to the severest drought, by a course of cultivation
which has been rendered possible only by under-draining. The lawns of the
Central Park, which are a marvel of freshness, when the lands about the
Park are burned brown, owe their vigor mainly to the complete drainage of
the soil. What is true of these thoroughly cultivated lands, it is
practicable to attain on all soils, which, from their compact condition,
are now almost denuded of vegetation in dry seasons.

*Porosity or Mellowness.*--An open and mellow condition of the soil is
always favorable for the growth of plants. They require heat, fresh air
and moisture, to enable them to take up the materials on which they live,
and by which they grow. We have seen that the heat of retentive soils is
almost directly proportionate