erent
regions of the globe affords results more to be depended upon in the
present state of our knowledge than those relating to the animal
kingdom, because the science of botany is more advanced, and probably
comprehends a great proportion of the total number of the vegetable
productions of the whole earth. Humboldt, in several eloquent passages
of his Personal Narrative, was among the first to promulgate
philosophical views on this subject. Every hemisphere, says this
traveller, produces plants of different species; and it is not by the
diversity of climates that we can attempt to explain why equinoctial
Africa has no Laurinae, and the New World no Heaths; why the Calceolariae
are found only in the southern hemisphere; why the birds of the
continent of India glow with colors less splendid than the birds of the
hot parts of America: finally, why the tiger is peculiar to Asia, and
the ornithorhynchus to New Holland.[842]

"We can conceive," he adds, "that a small number of the families of
plants, for instance, the Musaceae and the Palms, cannot belong to very
cold regions, on account of their internal structure and the importance
of certain organs; but we cannot explain why no one of the family of
Melastomas vegetates north of the parallel of thirty degrees; or why no
rose-tree belongs to the southern hemisphere. Analogy of climates is
often found in the two continents without identity of productions."[843]

The luminous essay of De Candolle on "Botanical Geography" presents us
with the fruits of his own researches and those of Humboldt, Brown, and
other eminent botanists, so arranged, that the principal phenomena of
the distribution of plants are exhibited in connexion with the causes to
which they are chiefly referrible.[844] "It might not, perhaps, be
difficult," observes this writer, "to find two points, in the United
States and in Europe, or in Equinoctial America and Africa, which
present all the same circumstances: as, for example, the same
temperature, the same height above the sea, a similar soil, an equal
dose of humidity; yet nearly all, _perhaps all_, the plants in these two
similar localities shall be distinct. A certain degree of analogy,
indeed, of aspect, and even of structure, might very possibly be
discoverable between the plants of the two localities in question; but
the _species_ would in general be different. Circumstances, therefore,
different from those which now determine the _stations_, have ha