North America and
are missing in intermediate countries, deserves our deepest interest....
These plants are relics of the Tertiary period, during which North America
and Europe still formed a continuous floral area. While the plants, on
which the fungus grew, differentiated into two closely related species, in
two at present widely separated but formerly connected radii of
distribution, the parasitical Exobasidium remained outwardly unaltered.
This is exactly like the case of another fungus, _Uromyces glycyrrhizae_,
which I have described and explained in the 'Berichten der Deutschen
Botanischen Gesellschaft' (Bd. VII, 1890, S. 377-384). _Exobasidium disc._
is also a parasitical fungus which has been growing on the parent form of
_Rhododendron viscosum_ and _Rhododendron flavum_ ever since that period
when North America and Europe were continuous and possessed the same
flora."

I am also indebted to Professor Magnus and to Dr. Levier for the following
names of closely allied species of plants which are found in America and
Asia only, it being particularly noticeable that it is in Asia Minor and
the Caucasus mountains that the relatives of the American species are most
frequently met with.

_Platanus occidentalis_: North America.
_Platanus orientalis_: Asia Minor.
_Liquidambar styraciflua_: North America.
_Liquidambar styraciflua_: Asia.
_Rhododendron viscosum_: North America.
_Rhododendron flavum_: Caucasus Mts.
_Rhododendron maximum_: North America.
_Rhododendron ponticum_: Causasus Mts.

Professor Magnus has, moreover, recently pointed out that the fungus
Uropyxis, which is a widespread American species and grows in Mexico, has
a representative in Manchuria. In his monograph on Uropyxis, Professor
Magnus enumerates further species of fungi which occur in America and Asia
only and are missing in other portions of the world (P. Magnus, Berichten
der Deutschen Botanischen Gesellschaft, Jahrgang 1899. Band XVII, Heft 3).

Referring the reader to Professor Edward S. Morse's trite article, Was
Middle America peopled from Asia? (Appleton's Popular Science Monthly,
November, 1898), I cite, from this, the following authoritative
statements: "From the naturalist's standpoint the avenues have been quite
as open for the circumpolar distribution of man as they have been for the
circumpolar distribution of other animals and plants, down to the minutest
land snail and low fungus. The ethnic resemblances supposed to exist
bet