en;--different ways of improving and
increasing the goodness of the soil.

"The foods that are necessary and essential to plants and most likely to
be lacking in the soil are nitrogen, potash and phosphorus. Now by no
means must you think that these are the only chemicals which are foods,
for there are something like thirteen, all of which do a share in the
food supply. Oxygen and carbon are very necessary indeed. Oxygen is both
in the air and in water. Carbon plants take entirely from the air. I
might go on and tell you of iron, of sulphur, of silicon and all the
others. But you would only get confused, so I am going to make you
acquainted with these three entirely necessary ones. They are
capricious; often missing, and when not missing hard to make into
available food for plants.

"The soil contains many bacteria, small living organisms. These may be
divided into two classes, the good ones and the bad ones. The good ones
acting on nitrogenous matter put it in shape for the plant to absorb or
feed upon. You see nitrogen may be in soil in quantities sufficient for
nourishment. But unless it is in a compound available for use, it is of
no value to the plant. Then there are the bad bacteria which act upon
nitrogen in such a way as to form compounds which escape from the soil
as a gas. That is pretty bad, is it not?

"How can the good bacteria be encouraged to grow, and the bad ones
prevented from forming? The necessary conditions for the growth of good
bacteria are air, water, darkness, humus matter and freedom from acid
condition of the soil. If the soil is acid then these other 'chaps' set
up their work; so we must see to it that our soils are well cultivated,
well aired, have plenty of manure, and, if acid, have a liming, so that
these bacteria missionaries can start their good work.

"The manure I spoke of above is the great source of nitrogen upon which
most plants depend. There is nitrogen sufficient right in the air, but
that again is not available. Certain plants like beans, peas and clovers
belonging to the family of legumes are a great deal more fortunate than
the rest of the plant families, for, under favourable conditions, they
develop bacteria which make it possible to take into themselves free
nitrogen. Just look here! See this narrow box; I can drop down one side
of it. Here is a sheet of glass put on so you may look at the roots of
the beans which are planted close to this glass side. Just observe the