Obviously they must have been subjected to widely
changing conditions. The fact of their stability through all these
outward changes is the best proof that the ordinary external conditions
do not necessarily have an influence on specific evolution. They may
have such a result in some instances, in others they obviously have not.
Many arctic forms bearing the specific name of _alpinus_ justify this
conclusion. _Astragalus alpinus_, _Phleum alpinum_, _Hieracium alpinum_
and [697] others from the northern parts of Norway may be cited as
examples.
Thus Primula imperialis has been found in the Himalayas, and many other
plants of the high mountains of Java, Ceylon and northern India are
identical forms. Some species from the Cameroons and from Abyssinia have
been found on the mountains of Madagascar. Some peculiar Australian
types are represented on the summit of Kini Balu in Borneo. None of
these species, of course, are found in the intervening lowlands, and the
only possible explanation of their identity is the conception of a
common post-glacial origin, coupled with complete stability. This
stability is all the more remarkable as nearly allied but slightly
divergent forms have also been reported from almost all of these
localities. Other evidence is obtained by the comparison of ancient
plants with their living representatives.
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