for the plant-food of cereals which are not endowed with the
faculty of encouraging those bacteria which fix nitrogen. High hopes
have been based upon the prospects of inoculating the soil over wide
areas of land with small quantities of sandy loam, taken from patches
cultivated for leguminous plants which have been permitted to run to
seed, thus multiplying the nitrogen-fixing bacteria enormously. The
main idea has been to encourage the rapid production of these minute
organisms in places where they may be specially useful, but in which
they do not find a particularly congenial breeding ground.

The hope that any striking revolution may be brought about in the
practice of agriculture by a device of this kind must be viewed in the
light of the fact that, while the scientists of the nineteenth century
have demonstrated, partially at least, the true reason for the
beneficial effects of growing leguminous plants upon soil intended to
be afterwards laid down in cereals, they were not by any means the
first to observe the fact that such benefits accrued from the practice
indicated. Several references in the writings of ancient Greek and
Latin poets prove definitely that the good results of a rotation of
crops, regulated by the introduction of leguminous plants at certain
stages, were empirically understood. In that more primitive process of
reasoning which proceeds upon the assumption _post hoc, ergo propter
hoc_, the ancient agriculturist was a past-master, and the chance of
gleaning something valuable from the field of common observation over
which he has trod is not very great.

Modern improvements in agriculture will probably be, in the main, such
as are based upon fundamental processes unknown to the ancients. By
the word "processes" it is intended to indicate not those methods the
scientific reasons for which were understood--for these in ancient
times were very few--but simply those which from long experience were
noticed to be beneficial. Good husbandry was in olden times clearly
understood to include the practice of the rotation of crops, and the
beneficial results to be expected from the introduction of those crops
which are now discovered to act as hosts to the microbes which fix
atmospheric nitrogen were not only observed, but insisted upon.

From a scientific point of view this concurrence of the results of
ancient and of modern observation may only serve to render the
bacteriology of the soil more interesting