roots, instead of being forced to spread themselves along the
surface-soil, and thus take up a large amount of room, will find no
difficulty in striking downwards. Two or three plants may thus be
enabled to grow in a thoroughly tilled soil in the same space as only
one could before tillage.

_American and English Farming._

The above considerations throw considerable light on what seems to many
farmers a strange anomaly--viz., the fact that the return of farm
produce per acre on American farms is, as a rule, very much less than
that from our own impoverished soils in this country. To many, at first
sight, this seems to be in direct contradiction to our common belief,
and to point to the conclusion that the virgin soils of America are,
after all, actually inferior in fertility to the soils of Britain.

It is not, however, necessary to draw this conclusion, as the facts of
the case admit of another explanation. The inferior returns obtained
from American farms are due, not to the fact that the American soil is
less fertile than the British--for this is not true--but to the fact
that it is less _intensively_ cultivated.

In America land is cheap and labour is dear; it is consequently found to
be more economical to cultivate a large tract of land less thoroughly
than a small area more thoroughly. In Britain the reverse is the case,
labour being cheap and land being dear. It is thus necessary to make the
land go as far as possible, and produce as heavy a crop as it is
possible to produce. There can be little doubt, that were American
farming to be carried on as intensively as is British farming, the
present yield would be at least probably doubled.

We have now to consider the second class of properties which influence
the fertility of a soil. These are _chemical_.

=II. Chemical Composition of a Soil.=--Chemically considered, the soil
is a body of great complexity. It is made up of a great variety of
substances. The relations existing between these substances and the
plant are not all of equal importance; some--and these form by far the
largest proportion of the soil-substance--are concerned in acting simply
as a mechanical support for the plant, and in helping to maintain those
physical properties in the soil which, as we have just seen, exercise
such important functions in the plant's development.

_Fertilising Ingredients._

A small portion of the soil-substance, however, takes a very much more
active part