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46 NEW HOLLAND IN EUUOPK. 
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plants over land ami sea. By adopting tlie first alternative we have 
to assume th:U, at the same geological period, New Holland as 
well as Europe produced the genus of identical, or very nearly iden- 
tical plants. An identity of climate, which, under any circum- 
stances, must be granted, would seera to settle the question by the 
adoption of this hypothesis in the most simple manner. And why 
should not similar, or even perfectly identical plants originate in two 
or several parts of the globe, provided external circumstances are fa- 
vourable?^ Theoretically speaking, there is, indeed, nothing to oppose 
to this, provided that the origin of species is brought about exclusively 
by external circumstances. But we are led to quite an opposite view 
by what we know of the distribution of existing plants. We know 
that every species — as a collection of countless individuals related 
by their mutual descent — was originally Uiore or less confined to a cir- 
cumscribed space, whence it spread centrifu;^-ally. However extensive 
the range of certain plants may be, it has always a well-defined limit, 
beyond which the species seldom ventures in isolated pntches. Wher- 
ever we do meet with such exceptional cases, similar to those of the 
enclaves in the distribution of languages, we have no difficulty in recog- 
nizing iu them intruders, or as parts cut off from the principal stock, 
and geology has already, in some respects, accounted for the cause of 
this disraembermcut. But not a single species has as yet been found 
occupying two distinct territories which are evidently the result of two 
centres of creation. These focts justify us in rejecting the proposition 
of a contemporaneous origin of identical or nearly identical species, hi 
two countries most widely separated from each other, and that of a 
common origin of the floras of Europe and New Holland. Nothing 
remains but to assume that either the New Holland plants emigrated 
to Europe, or (what is less probable) the former European plants which 
had an Australian character passed from Europe to New Holland. 
Wandering is the destiny of mortals. If man or beast are com- 
pelled to leave their native place, their organization and the nature of 
surrounding circumstances easily supply us with an intelligible reason 
for the act. But it is more difEcult to account for the migration of plants, 
intimately connected as they are with the soil ; and if, nevertheless we 
find them effecting a migration from one continent to the other, it can 
only be the result of a tendency belonging less to the individual than 
to the whole species, desirous to preserve its existence. If it be inter- 
