y from a drying up of
the soil, seems to me to point to the correctness of the view I have
expressed on several occasions, that these plants have originated long
before the Glacial period at a time when the climate was warmer and
moister than it is now. It seems quite natural to Dr. Christ that the
Arcto-Alpine flora should have originated in Asia, but he excepts thirty
species which are absent from Northern Asia, though occurring in America
(p. 327). These he thinks have penetrated direct from America to the
Alps by way of Scandinavia, since no less than twenty-three still occur
in the latter country. In the human population of the Alps, he continues
(p. 336), one can distinguish an indigenous Celtic race, a Germanic
colder and more apathetic race, and a more lively Roman one. The flora
is composed of quite a similar mixture. We find also an indigenous
element--an Arctic and a Mediterranean one. The last element is a
survival of the Tertiary flora of the Central European plateau (p. 532).
The plants were driven down to the shores of the Mediterranean, and it
is only after the retreat of the glaciers that a few of them have been
able to regain their ancient territory. The incoming Asiatic and North
American flora likewise retired at the end of the Glacial period to the
Alps and the Arctic countries, and left isolated traces of its former
abundance on the North European plain. The bulk of the Arctic or Alpine
flora is held to be of Asiatic origin. Since Siberia shows little trace
of having been glaciated, owing to the dryness of the climate, a rich
flora was able to develop there, which spread into Europe as soon as the
vanishing glaciers made room for it.

These are the views of Professor Engler and Dr. Christ. They agree in so
far as both of them maintain that the bulk of the Alpine flora is
post-glacial--that is to say, that it has developed quite recently, or
migrated to the Alps after the glaciers had retreated from the plain to
the mountain recesses. It is assumed by Dr. Christ that while Europe was
practically uninhabitable, a rich flora survived in Northern Asia,
because the climate there was too dry for the development of glaciers.
Due consideration in this interesting speculation, however, is not given
to the fact which he himself emphasised, that Alpine plants are
particularly prone to suffer from a dry climate. Even a moderately dry
cold kills most of them. How can we then reconcile this fact with the
theory