Animals, on the contrary, can at pleasure migrate from
the equator toward the poles; and this they can more especially doo where
the isothermal lines are much inflected, and where hot summers succeed a
great degree of winter cold. The royal tiger, which in no respect differs
from the Bengal species, penetrates every summer into
p 350
the north of Asia as far as the latitudes of Berlin and Hamburg, a fact of
which Ehrenberg and myself have spoken in other works.*
[footnote] *Ehrenberg, in the 'Annales des Sciences Naturelles', t. xxi.,
p. 387, 412; Humboldt, 'Asie Centrale', t. i., p. 339-342, and t. iii., p.
96-101.
The grouping or association of diffrent vegetable species, to which we are
accustomed to apply the term 'Floras', do not appear to me, from what I have
observed in different portions of the earth's surface, to manifest such a
predominance of individual families as to justify us in marking the
geographical distinctions between the regions of the Umbellatae, of the
Solidaginae, of the Labiatae, or the Scitamineae. With reference to this
subject, my views differ from those of several of my friends, who rank among
the most distinguished of the botanists of Germany. The character of the
floras of the elevated plateaux of Mexico, New Granada, and Quito, of
European Russia, and of Northern Asia, consists, in my opinion, not so much
in the relatively larger number of the species presented by one or two
natural families, as in the more complicated relations of the coexistence of
many families, and in the relative numerical value of their species.
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