of the soil. If, however, the supply of
water be too great, as is the case when a spring gains admission
into the soil, or when the sinking of the fluid through the canals
to a sufficient depth below the surface is prevented, it is clear
that these also must get filled with water so soon as the pores
have become saturated. This, then, is the condition of _undrained
soil_.

"Not only are the pores filled, but the interstitial canals are
likewise full; and the consequence is, that the whole process of
the germination and growth of vegetables is materially interfered
with. We shall here, therefore briefly state the injurious effects
of an excess of water, for the purpose of impressing more strongly
on your minds the necessity of thorough-draining, as the first and
most essential step towards the improvement of your soil.

"The _first_ great effect of an excess of water is, that it
produces a corresponding diminution of the amount of air beneath
the surface, which air is of the greatest possible consequence in
the nutrition of plants; in fact, if entirely excluded, germination
could not take place, and the seed sown would, of course, either
decay or lie dormant.

"_Secondly_, an excess of water is most hurtful, by reducing
considerably the _temperature_ of the soil: this I find, by careful
experiment, to be to the extent of six and a-half degrees
Fahrenheit in Summer, which amount is equivalent to an elevation
above the level of the sea of 1,950 feet.

"These are the two chief injuries of an excess of water in soil
which affect the soil itself. There are very many others affecting
the climate, &c.; but these not so connected with the subject in
hand as to call for an explanation here.

"Of course, all these injurious effects are at once overcome by
thorough-draining, the result of which is, to establish a direct
communication between the interstitial canals and the drains, by
which means it follows, that no water can remain any length of time
in these canals without, by its gravitation, finding its way into
the drains.

"The 4th Fig. indicates badly-cultivated soil, or soil in which
large unbroken clods exist; which clods, as we have already seen,
are very little better than stones, on account of their
impermeability to air and t