EXISTING VEGETABLE CREATION. 323 
especially of Dr. Hooker, in his expedition to the South Pole, have 
not only confirmed former instances, but added others. The number of 
such recurring species is much increased, if flowerless and leafless plants 
(Cryptogams) are taken into account. These exhibit very many instances 
of species which the remotest parts of the globe have in common, 
and which fail altogether in the intervening countries. And yet there 
exists no ground for assuming, that this sort of plants is endowed 
with greater facilities of migration ; although it is intelligible, that the 
more simple organizations are produced spontaneously with greater ease, 
than others more compound. Neither do we find, that plants, whose 
fruits and seeds would render them more capable of migration, are 
particularly common to distant regions. A strong argument against 
any great influence of migration is likewise derived from the fact, that 
the floras of the antediluvian world seem to have corresponded more 
closely among themselves, than those at present existing do ; although 
there was then less land—and_ perhaps only islands—rendering migra- 
tion a process of greater difficulty. Further: the analogy or difference - 
between existing floras, stands in no proportion to the facilities, or other- 
wise, of migration; although their influence cannot be denied, for 
instance, in the occasional scantiness of plants in small islands, 
very distant from continents. Even with respect to those tracts 
which offer no impediments to the influence of migration, —for - 
instance, between the west coast of France and the Ural,—it is 
difficult to suppose this vast territory to have continued a desert, 
until the vegetation common to both those countries accomplished 
its migration from the one extreme point to the other of this enor- 
mous plain, or from the centre to either. 
Those who assume that one single parent plant has produced the 
countless individuals of each species, seem to forget that the idea 
of species cannot assuredly be extended to the lowest plants and 
animals, such as Lichenes, Alge, and Zoophytes; and that even among 
the higher orders of plants (perhaps, also of animals) the limitation 
of species depends frequently upon the particular views entertained 
by naturalists. Among mammalia, it is difficult to conceive that 
there can have existed originally more than one parent species ; 
rather the reverse seems to have been the case ; America, for example, 
and the continent of Europe have uo species in common; no hares, — 
moles, or squirrels occur in Ireland ; no moles on the island of Mona ; 
272 
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