cial period (p. 109). In speaking of the
Caucasus, Professor Engler informs us (p. 117) that a good many species
which do not occur in the Alps reached these mountains from Siberia.
Apart from the northern glacial plants, the Caucasus has only few
species in common with the Alps, more with the Balkan mountains and
Northern Persia. Turning to Afghanistan, our author mentions (p. 121) a
few Alpine plants as occurring in that country, and likewise in the
Caucasus and the Himalayas. He considers it probable that the route of
migration of some glacial plants from the east to the west, and _vice
versa_, lay across the Afghan mountains. Many of our Alpine plants occur
in the Siberian mountains, but in the Altai and Eastern Siberia
generally a considerable number of these are by no means confined to the
mountains (p. 125). They are also met with in the lower regions, and the
rare Alpine Edelweiss (_Leontopodium alpinum_) frequently covers wide
tracts in the plain, and is passed by almost unnoticed by the Siberian
botanist.

Special attention is drawn by Professor Engler to the fact (p. 130) that
several of the Siberian plants inhabit the Alps and the Caucasus, but
are not found in Scandinavia. And from this he deduces the conclusion
that part of the Siberian flora migrated in a south-westerly direction
towards the Caucasus and the mountains of the Mediterranean area,
exactly in the manner indicated in respect to the fauna of the Alps. We
learned that the migration to the Alps from Central and perhaps also
parts of Northern Asia took a south-westerly course first, and was then
followed by one in an easterly direction. I called the former the
Oriental migration and the latter the Siberian. Later on Professor
Engler states (p. 142) that the main mass of the Siberian forms of
plants certainly wandered westward to the south of the Ural. This is
proved by the numerous glacial plants found in the Caucasus, while the
glacial flora of the Ural Mountains is poor. Finally, he expresses the
opinion that the probability of most of the Alpine plants occurring in
Arctic Siberia, having wandered from the Alps, by way of Scandinavia,
Greenland, and North America, to North-eastern Siberia, is greater than
the direct migration from Europe to Siberia (p. 143).

Another continental writer on the Alpine flora who deserves special
mention is Dr. Christ. His observation that Alpine plants by no means
suffer from a high temperature (p. 309), but solel