ants will not always answer for the growth of
another member of the same. But in some instances it is thought that it
will answer. The study of this phase of the question has not yet
progressed far enough to reflect as much light upon it as could be
desired. It is certainly known, however, that alfalfa will grow on soils
that grow burr clover (_Medicago maculata_) and sweet clover (_Melilotus
alba_), hence the inference that soil from fields of either will
inoculate for alfalfa.

Nitragin is the name given by certain German investigators to a
commercial product put upon the market, which claims to be a pure
culture of the root tubercle organism. These cultures were sold in the
liquid form, and it was customary when using them to treat the seed with
them before it was planted. Their use has been largely abandoned,
because of the few successes which followed their use compared with the
many failures. But it is now believed that these cultures can be
prepared and used so as to be generally effective and without excessive
cost to the grower.

In preparing cultures it has been found that by gradually reducing the
amount of nitrogen in the culture of media, it is possible to increase
the nitrogen fixing power in these germs from five to ten times as much
as usually occurs in nature. It is now known that the bacteria thus
grown upon nitrogen free media retain high activity if carefully dried
and then revived in liquid media at the end of the varying lengths of
time. Some absorbent is used to soak up the tubercle-forming organisms.
The cultures are then allowed to dry, and when in that condition they
can be safely sent to any part of the country without losing their
efficacy. It is necessary to revive the dry germs by immersing them in
water. By adding certain nutrient salts the bacteria are greatly
increased if allowed to stand for a limited time--as short, in some
instances, as 24 hours. The culture thus sent out in a dry form, and no
larger than a yeast cake, may thus be made to furnish bacteria
sufficient to inoculate not less than an acre of land. It is stated that
the amount of inoculating material thus obtained is only limited by the
quantity of the nutrient water solution used in increasing the germs, so
that the cost of inoculating land by this process is not large. The
culture may be applied by simply soaking the seed in it, by spraying the
soil, or by first mixing the culture into earth, spreading it over the
field