cannot very well elsewhere, or the plant roots might {83}
become too cold. If there is frost during the winter both farmer and
gardener are pleased because they say the frost "mellows" the ground;
you can see what they mean if you walk on a frosty morning over a
ploughed field. The large clods of earth are no longer sticky, they
already show signs of breaking up, and if they are not frozen too hard
can easily be shattered by a kick. The change has been brought about
in exactly the same way as the bursting of water-pipes by frost. When
water freezes it expands with enormous force and bursts open anything
that confines it; water freezing in the pores of the soil forces the
little fragments apart. This action is so important that further
illustrations should be looked for. A piece of wet chalk left out on a
frosty night often crumbles to pieces. It is dangerous {84} to climb
cliffs in the early spring because pieces of rock that have been split
off during the winter frosts by the expanding water may easily give
way. Frost plays havoc with walls built of flints and with old bricks
that are beginning to wear. If there are several frosts, with falls of
rain or snow and thaws coining in between, the soil is moved about a
good deal by the freezing and melting water. Bulbs and cuttings are
sometimes forced out of the ground, whilst grass and young wheat may be
so loosened that they have to be rolled in again as soon as the weather
permits. When the ground has been dug in autumn and left in a very
rough state all this loosening work of the frost is very much helped,
because so much of the soil may become frozen. If in spring you dig a
piece of land that has already been dug in autumn, and then try digging
a piece that has not, you will find the first much easier work than the
second in all but very sandy soils.

A little before the seeds are sown, the soil has to be dug or
cultivated again so that it may become more level and broken into
smaller pieces. The farmer then harrows and the gardener rakes it, and
it becomes still finer. Very great care is bestowed on the preparation
of the seed bed, and it will take you longer to learn this than any
other part of outdoor gardening. The soil has to be made fine and dry,
and no pains must be spared in getting it so.

When at last the soil is fine enough the seed is put in. But it is not
enough simply to let the seed tumble into the ground. It has to be
pressed in gentl