S e c t io n V.—Recapitulation and conclusion*
We may now compare the results which arise from the facts
stated in this chapter^ with thé three suppositions laid down in
-the/outset, respecting the origin of plants.
In the first place it is obvious that the hypothesis of Linnaeus,
which represents mil plants whatever as originating
from a common centre, is wholly irreconcilable with the phenomena.
I t is unnecessary to say any .thing further on this
p a rt of the subject. - We have seen, that various parts o f the
world, remotely separated, possess'-each of them a vegetable
kingdom in a great measure, at least, peculiar and distinct
from the productions of other countries.
The same eönsiderations are, perhaps, equally conclusive
against the third hypothesis, that the species .-;«f plants are
universally diffused wherever climates and physfe^ condi-
ritesiiLgeneral are congenial to their existence »and propaga*
tion. This opinion, which has been held h y many emmeni
naturalists, seems to be most clearly refuted by the following
arguments.
1. I t would be easy to discover districts, situated respectively
in North America and in Europe, or in.equinoe->
rial America, Africa, asdr Asia, in which all the came
physical conditions exist, namely, a parallel .temperature and
elevation, a similar soil, and the same degrees of humidity in
the atmosphere; yet the species of plants in these sev^al;
districts will be far from being identical. The vegetable tribes
will present, in each respectively, analogies of form and general
character; but few, if any, o f the same species will be found
in localities thus separated.*
2. Instances may frequently be observed in which plants-
become naturalized in countries where theydiad never existed*
until they were conveyed by human agency, or by the accidental
transportation of seeds. When this has once happened
the results proye, that the climate and all, external
* Vide De Candolle, ubi supra, p.402.
conditions are perfectly congenial to their nature, since they
have' spread, in a^short time/oVer éxtensivé régions, and havé
appeared po supplant,xin’some plages;,, fthe, indigenous tribes.
Previously to thè importation of seeds; the physical conditions
locally present had ho'power of producing sûeK plants ; nor
ddes it ^ p e a r , th a t their qxistencè' is'l>sb Connected with external
conditions as to have been5 from the' origin-'df things
necessarily or riaturally’co-êiténsivè; With them: When introduced
they multiply just? dé horses and ôden from Europe
have produced, herds which1 cover thé immense plains of Pa^
raguay;
It appears, then, that&he . phenomena connected with thé
distribution' of" plants ate* only "reconcilable with- oUe;%’pb| I
thesis; or rather they lead tis felearlyWone ‘inference ; namely,
that the Vegetable creation was originally divided into a: limited
number of provinces;' Each country'had its peculiar
tribeSTWhich at first. éXfâlîed not eTsèwhérâf This''conclusion
results most distinctly frbm the general difference irfühë1 Species
belonging' to each1 Of the great-: continents a difference
never called in question >in fCspeCt’to the principal- massés" Of
végétation, and the great'aggregate numbers'Of plants Wbifch,
by their^situation Rt'a distancé frotn sèa-cOasts, arid^by thé
nature of theii* seeds; are remöyêdffroöilhe'chances of transportation
; and, secondly, from the affangeméntöf'grègUrioUs
plants' round sonaeparticular foci/the individual species being
spread out in vâriôüs directions With reference to the central
points.' :
If We now revert to the question, of what ffature are the
exceptions to this général infèfëncé ,- or whether im p ro b ab le !
that the plants whiph -aVe; found in different botàméàl provinces
wëre indigenous in all of them, or have been dispersed
from one original lênt> the following considerations' dèduéed
from fkets already stirvêyéd, tffl'I pôifft ^.-wKich
is' the probable édnclhsiöh. - 1 *
1. That there are natural provisions for the dispersion of
plants, and causes actually1 in öpératiöh Which have this
result.
2. That -the species of plants are widely spread or ree
2