to the completeness with which their free
water is removed by underground draining, and that, by reason of the
increased facility with which air and water circulate within them, their
heat is more evenly distributed among all those parts of the soil which
are occupied by roots. The word _moisture_, in this connection, is used in
contradistinction to _wetness_, and implies a condition of freshness and
dampness,--not at all of saturation. In a saturated, a soaking-wet soil,
every space between the particles is filled with water to the entire
exclusion of the atmosphere, and in such a soil only aquatic plants will
grow. In a _dry_ soil, on the other hand, when the earth is contracted
into clods and baked, almost as in an oven,--one of the most important
conditions for growth being wanting,--nothing can thrive, save those plants
which ask of the earth only an anchoring place, and seek their nourishment
from the air. Both air plants and water plants have their wisely assigned
places in the economy of nature, and nature provides them with ample space
for growth. Agriculture, however, is directed to the production of a class
of plants very different from either of these,--to those which can only
grow to their greatest perfection in a soil combining, not one or two
only, but all three of the conditions named above. While they require
heat, they cannot dispense with the moisture which too great heat removes;
while they require moisture, they cannot abide the entire exclusion of
air, nor the dissipation of heat which too much water causes. The interior
part of the pellets of a well pulverized soil should contain all the water
that they can hold by their own absorptive power, just as the finer walls
of a damp sponge hold it; while the spaces between these pellets, like the
pores of the sponge, should be filled with air.

In such a soil, roots can extend in any direction, and to considerable
depth, without being parched with thirst, or drowned in stagnant water,
and, other things being equal, plants will grow to their greatest possible
size, and all their tissues will be of the best possible texture. On rich
land, which is maintained in this condition of porosity and mellowness,
agriculture will produce its best results, and will encounter the fewest
possible chances of failure. Of course, there are not many such soils to
be found, and such absolute balance between warmth and moisture in the
soil cannot be maintained at all times, a