; it is much less common now
that crops like mangolds and swedes are grown, which can, if necessary,
be hoed all the summer.

[Illustration: Fig. 44 _b_. Untouched plot, many weeds]

We have already seen (p. 69) that ordinary cultivated plants will not
live in a water-logged soil. {96} Wherever there is an excess of water
it must be removed before satisfactory results can be obtained. Fig.
46 shows a field of wheat in May where the crop is all but killed and
only certain weeds survive on a patch of undrained land that lay wet
all the winter. Draining land is difficult and somewhat expensive;
trenches are first cut to a proper depth, and drain pipes are laid on
the bottom, taking care that there is a gentle slope all the way to the
ditch. The rain soaks into the soil and gets into the pipes, for they
are not joined together like gas or water pipes, but left with little
spaces in between; it then runs out into the ditch. Usually only clay
soils need drainage, but occasionally sandy soils do also (see pp. 30,
106). A great deal of drainage was carried out in England between 1840
and 1860, and it led to a marked improvement in agriculture and in
country life generally. There is, however, a great deal that wants
doing now.

[Illustration: Fig. 45. A plot of wheat left untouched since 1882 at
Rothamsted has now become a dense thicket]

The addition of chalk or lime to soil was found in Chap. III. to
improve it very much by making it less sticky and less impervious to
air and water. Chalk or lime does more than this. It puts out of
action certain injurious substances or acids that may be formed, and
thus makes the conditions more favourable for plants and for the useful
micro-organisms; farmers and gardeners express this by saying that it
"sweetens the soil." A United States proverb runs: "A lime country is
a rich country." Very many soils in England are improved by adding
lime or chalk. There are considerable areas in the south-eastern and
eastern counties where the soil is very chalky; here you find a
wonderfully rich assortment of flowers and shrubs. Where there is too
much chalk the soil is not fertile, because it lets water {98} through
too easily, as was shown on p. 26: but for this very reason it is
admirable for residential purposes.

There are some exceptions to the rule that plants need lime. Some
plants will not tolerate it at all; such are rhododendrons, azaleas,
foxgloves, spurrey, and broo