hered kind to the most
passionate fondness, is the occasion of an equal dispersion of birds over
the face of the earth. Without this provision one favourite district
would be crowded with inhabitants, while others would be destitute and
forsaken. But the parent birds seem to maintain a jealous superiority,
and to oblige the young to seek for new abodes; and the rivalry of the
males in many kinds, prevents their crowding the one on the other.
Whether the swallows and house-martins return in the same exact number
annually is not easy to say, for reasons given above; but it is apparent,
as I have remarked before in my Monographies, that the numbers returning
bear no manner of proportion to the numbers retiring.

LETTER XL.

SELBORNE, _June_ 2_nd_, 1778.

Dear Sir,--The standing objection to botany has always been, that it is a
pursuit that amuses the fancy and exercises the memory, without improving
the mind or advancing any real knowledge; and, where the science is
carried no farther than a mere systematic classification, the charge is
but too true. But the botanist that is desirous of wiping off this
aspersion should be by no means content with a list of names; he should
study plants philosophically, should investigate the laws of vegetation,
should examine the powers and virtues of efficacious herbs, should
promote their cultivation; and graft the gardener, the planter, and the
husbandman, on the phytologist. Not that system is by any means to be
thrown aside; without system the field of Nature would be a pathless
wilderness; but system should be subservient to, not the main object of,
pursuit.

Vegetation is highly worthy of our attention; and in itself is of the
utmost consequence to mankind, and productive of many of the greatest
comforts and elegances of life. To plants we owe timber, bread, beer,
honey, wine, oil, linen, cotton, etc., what not only strengthens our
hearts, and exhilarates our spirits, but what secures us from
inclemencies of weather and adorns our persons. Man, in his true state
of nature, seems to be subsisted by spontaneous vegetation; in middle
climes, where grasses prevail, he mixes some animal food with the produce
of the field and garden; and it is towards the polar extremes only that,
like his kindred bears and wolves, he gorges himself with flesh alone,
and is driven to what hunger has never been known to compel the very
beasts, to prey on his own species.

The productions