It should, however, be observed that these
plants are not strictly arctic forms; for, as Mr. H.C. Watson has remarked,
"in receding from polar toward equatorial latitudes, the Alpine or mountain
flora really become less and less Arctic." Besides these identical and
closely allied forms, many species inhabiting the same widely sundered
areas, belong to genera not now found in the intermediate tropical
lowlands.
These brief remarks apply to plants alone; but some few analogous facts
could be given in regard to terrestrial animals. In marine productions,
similar cases likewise occur; as an example, I may quote a statement by the
highest authority, Prof. Dana, that "it is certainly a wonderful fact that
New Zealand should have a closer resemblance in its crustacea to Great
Britain, its antipode, than to any other part of the world." Sir J.
Richardson, also, speaks of the reappearance on the shores of New Zealand,
Tasmania, etc., of northern forms of fish. Dr. Hooker informs me that
twenty-five species of Algae are common to New Zealand and to Europe, but
have not been found in the intermediate tropical seas.
>From the foregoing facts, namely, the presence of temperate forms on the
highlands across the whole of equatorial Africa, and along the Peninsula of
India, to Ceylon and the Malay Archipelago, and in a less well-marked
manner across the wide expanse of tropical South America, it appears almost
certain that at some former period, no doubt during the most severe part of
a Glacial period, the lowlands of these great continents were everywhere
tenanted under the equator by a considerable number of temperate forms.
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