ned in the air found in the interstices; that is, the air spaces
between the particles of soil. This they store up in the nodules for the
use of the clover plants and also the crops that shall follow them.

The nodules in clover plants vary in size, from a pin head to that of a
pea, and they are frequently present in large numbers. Bacteria are
present within them in countless myriads. They gain an entrance into
the plant through the root hairs. The exact way in which benefit thus
comes to the clover plants is not fully understood, but it is now quite
generally conceded that the nitrogen taken in by these minute forms of
life is converted into soluble compounds, which are stored in the
tissues of the roots, stems and leaves of the plants, thus furnishing an
explanation to the increased vigor. It cannot be definitely ascertained
at present, if, indeed, ever, what proportion of the nitrogen in clover
is taken from the air and from the soil, respectively, since it will
vary with conditions, but when these are normal, it is almost certain
that by far the larger proportion comes from the air. But it has been
noticed that when soil is freely supplied with nitrogen, as in liberal
applications of farmyard manure, the plants do not form nodules so
freely as when nitrogen is less plentiful in the soil. The inference
would, therefore, seem to be correct, that when plants are well supplied
with nitrogen in the soil they are less diligent, so to speak, in
gathering it from the air. In other words, clover plants will take more
nitrogen from the air when the soil is more or less nitrogen hungry than
when nitrogen abounds in the soil. And yet the plants should be able to
get some nitrogen from the soil in addition to what the seed furnishes
to give them a vigorous start.

This power to form tubercles, and thus to store up nitrogen, is by no
means confined to clovers. It is possessed by all legumes, as peas,
beans and vetches. It is claimed that some of these, as soy beans, cow
peas and velvet beans, have even greater power to gather nitrogen from
the air and store it in the soil than clover, since the nodules formed
on the roots of these are frequently larger. In some instances, on the
roots of the velvet bean they grow in clusters as large as an ordinary
potato. With reference to all these leguminous plants it has been
demonstrated that under proper conditions good crops may be grown and
removed from the soil and leave it much richer