discovery of the greater number of these species*, after comparing
the proportion which the European species bear to
foreign kinds,"and endeavouring to estimate the extent of
countries scarcely examined • or as yet wholly unexplored,
and the probable number of the vegetable tribes which they
contain, the same writer has concluded that the plants already
collected are about half the existing number, and conseH
quently, that the total aggregate of species which- vegetate
on the earth, is between 1J 0,000 and 120,000:: a vast number,
which 'illustrates the admirable variety Of nature, and
proves that the laws of botanical geography rest as yet but on
an imperfect knowledge of the existing tribes. Theinforma-
tion, however, which has already been acquired of the different
assemblages of plants, or of the floras of particular
countries; is becoming every day more extensi ve, * and the
comparison of different regions in the vegetable world appeals
already to have furnished sufficient data for some very interesting
and satisfactory conclusions. On exploring with
greater accuracy the botany off countries distant from each
other, naturalists have become more and' more aware of the
fact, that, each region of the earth has its separate’botanical
creation, or if we may so speak, a select arrangement of yege-
tablespecies appropriately itself; and the greater the accuracy
of discrimination that h a sb ë en introduced into the inquiry,
the more strongly distinguished from each other have different
countries become, in the comparison of their respective aggregates
of plants. The data on which this conclusion., is
founded have been • accumulating for many years, and havé
been the work of many different contributors. • Link investigated
the flora of Northern Germany, and the calcareous
districts; * Thunberg explored the botany of the Capè, ‘Adan-
son, Smeathman, and others, th a t of inteftropical Africa;
M. De Candolle has made known, the vegetation of France,
Wahlenberg the vegetable productions of Lapland, of
Switzerland, and of the Carpathian chain: Pursh those
of North America; Robert Brown has explored the botany
of New Holland, and has elucidated the collection
of other botanists in Africa. But the science of botanical
geography is principally indebted to the comprehensive
and, philosophical? imind of M.< de Jlumboldt, Whose enlightened
genius has penetrated the Obscurities of so many regions
of science« » M. die Humboldt’s Essay on. the Geography.
of Plants was the first work, as M. De Candolle observes,!
which displayed :the real extent and relations of this
sciences.* In his subsequent works/dnd ' still more in his personal
-researchespthe same "writer has further contributed to
increase the tsum of knowledgeon ‘these, subjects,' of which
he: has displayed" the relations in almost brilliant manner in
bis Prolegomena' to the American Flora.-f* It wouldf.be‘foreign.
to^my purpose to trace the series* : of theses discoveries.
I shall merely state, in as brief a manner as possible, some
general results ’to be deduced from the researches of M. de
Humboldt, 'Mr. Robert Brown, M.' De Candolle, and other
writers, and poipt out their, relations to*the subject which I
have proposed to investigate.
Section Il.— Gener'ûi fac ts connected wiM the distribution
o f vëgeiable tribes—‘Distribution o f the great families or
''fia s s e s ' o f the lesser families of orders, and o f genera ;
- lastly, o f species.
Paragraph 1.—Distribution’ of Plants in. reference* to the
three great families'Or classes.
Among the most striking facts in Botanical Geography,
are th,p different p ro p o rtio n whi ch plants* of the three great
families bear to each other in different zpnes.^ The proportional
number of dicotyledonous plants increases as we approach
the equator, and diminishes towards the poles. Cellular
or acotyledonous plants follow an inverse ratio, and de-
* Essai sur la Géographie des Plantes, accompagné d’un tableau physique des
régions équinoxiales. Paris, 1805. '
+ See likewise his work, entitled “ De Distributione Geographica Plantarum
secundum coeli temperiem et altitudinem montium Prolegomena.” Paris, 1817.
X Mr. R. Brown was the first botanist who displayed the relations between the
three great divisions of the vegetable world. See Appendix to Flinders’ Voyage
to Terra Australis, and Observations on the Herbarium of the Congo, appended
to Tucker’s Voyage to the River Zaire, p. 422, 479. M. de Humboldt, in 1815,
followed the same method of research, extending it to different orders or natural
families.