tion of some
colder species which were everywhere expelled or destroyed.... We may
infer that, towards the close of the Tertiary epoch, the continuous
circumpolar land was covered with a vegetation also largely composed of
identical plants, but adapted to a warmer climate. As the climate became
less warm there would commence a migration southwards which would result
in the modified descendants of these plants being now blended with the
vegetation of central Europe and the United States. As the glacial period
gradually advanced, the tropical plants will have retreated from both
sides towards the equator followed in the rear by the temperate
productions and these by the arctic. When the climate of the earth again
ameliorated, the migration took place in a reverse direction and in this
way mountain ranges became the havens of refuge for the fragments of the
original arctic flora which were exterminated on the lowlands. An
indication of the great antiquity of the arctic alpine flora is afforded
by the fact of its absence in the comparatively modern volcanic mountains
of France.... If it be granted that the polar area was once occupied by
the Scandinavian flora and that the cold of the glacial epoch did drive
this vegetation downwards ... in arctic America ... where there was a free
southern extension and dilatation of land for the same Scandinavian plants
to occupy, these would multiply enormously in individuals...."

The following remarkable results of recent botanical research will be
found to be of profound interest to investigators and to support the
foregoing conclusions. Amongst the many important discoveries of hitherto
undescribed species of plants, made by the distinguished botanists Mr.
Stephen Sommier and Dr. Emile Levier during their expedition in the
Caucasus mountains, in 1890, was that of a species of fungus named
_Exobasidium discoideum_ Ell., which was found growing on the
_Rhododendron flaro_ L. This fungus was submitted to Prof. P. Magnus of
Berlin, who pronounced it to be the identical Exobasidium which has been
found growing on the _Azalea viscosa_ L. in New Jersey, U. S. A. The
following is the authoritative statement of Prof. P. Magnus which appears
in Messrs. S. Sommier and E. Levier's Enumeratorio plantarum caucas: acta
horti petropolitani, vol. XVI. St. Petersburg, 1899.

"The occurrence of the identical species of fungus on two closely related
plants, which respectively grow in the Caucasus and in