ly distinct animals and
plants, is a fact which has been familiar to all naturalists since
Buffon first pointed out the want of _specific_ identity between the
land quadrupeds of America and those of the Old World. The same
phenomenon has, in later times, been forced in a striking manner upon
our attention, by the examination of New Holland, where the indigenous
species of animals and plants were found to be, almost without
exception, distinct from those known in other parts of the world.

But the extent of this parcelling out of the globe amongst different
_nations_, as they have been termed, of plants and animals--the
universality of a phenomenon so extraordinary and unexpected, may be
considered as one of the most interesting facts clearly established by
the advance of modern science.

Scarcely fourteen hundred species of plants appear to have been known
and described by the Greeks, Romans, and Arabians. At present, more than
three thousand species are enumerated, as natives of our own
island.[841] In other parts of the world there have been now collected
(1846) upwards of 100,000 species, specimens of which are preserved in
European herbariums. It was not to be supposed, therefore, that the
ancients should have acquired any correct notions respecting what may be
called the geography of plants, although the influence of climate on the
character of the vegetation could hardly have escaped their observation.

Antecedently to investigation, there was no reason for presuming that
the vegetable productions, growing wild in the eastern hemisphere,
should be unlike those of the western, in the same latitude; nor that
the plants of the Cape of Good Hope should be unlike those of the south
of Europe; situations where the climate is little dissimilar. The
contrary supposition would have seemed more probable, and we might have
anticipated an almost perfect identity in the animals and plants which
inhabit corresponding parallels of latitude. The discovery, therefore,
that each separate region of the globe, both of the land and water, is
occupied by distinct groups of species, and that most of the exceptions
to this general rule may be referred to disseminating causes now in
operation, is eminently calculated to excite curiosity, and to stimulate
us to seek some hypothesis respecting the first introduction of species
which may be reconcileable with such phenomena.

_Botanical geography._--A comparison of the _plants_ of diff