If one digs up with great care a root of alfalfa (it need not be an old
plant, the youngest plant will show the same peculiarity), and care is
taken in exposing the root (perhaps the best method is the washing away
of the surrounding earth by water), some small nodules attached to the
fine, hair-like roots are easily distinguished by the naked eye, and
these nodules are the home of a teeming, microscopical, industrious
population, who perform their allotted work with the silent, persistent
energy so often displayed in Nature. Men of science have been able to
identify at least three classes of these bacteria, and to ascertain the
work accomplished by each. The reason for their existence would seem to
be that one class is able to convert the nitrogen in the air into
ammonia, whilst others work it into nitrite, and the third class so
manipulate it as to form a nitrate which is capable of being used for
plant food.
Now, although one ton of alfalfa removes from the soil 50 lb. of
nitrogen, yet that crop leaves the soil richer in nitrogen, because the
alfalfa has encouraged the multiplication of those factories which
convert some of the thousands of tons of nitrogen floating above the
earth into substance suitable for food for plant life.
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