___ problem of determining the reasons for this isolated distribution. 
152 Rhodora 
with those of the Arctic. And the occurrence in exposed or ir 
situations of Mt. Washington or along the Gaspé rivers of such isola 
species as Empetrum nigrum, Rubus Chamaemorus and Dryas Drw 
mondii is one of the strong links of evidence which has convi 
botanists of the inevitableness of the conclusions long ago reached 
by Hooker, Gray, and others, that it is “difficult to account for these 
facts, unless we admit Mr. Darwin’s hypotheses, first, that the existin 
Scandinavian flora is of great antiquity, and that previous to the glact 
epoch it was more uniformly distributed over the polar zone than 
is now; secondly, that during the advent of the glacial period this 
ndinavian vegetation was driven southward in every longitude, 
and even across the tropics into the south temperate zone; and thi 7 
on the succeeding warmth of the present epoch, those species that 
survived both ascended the mountains of the warmer zones, and also 
returned northward accompanied by aborigines of the countries 
had invaded during their southern migration. Mr. Darwin sh 
how aptly such an explanation meets the difficulty of accounting 
the restriction of so many American and Asiatic arctic types to MO 
own peculiar longitudinal zones, and for what is a far greater difficulty, 
the representation of the same arctic genera by most closely allied 
species in different longitudes.” : 
Practically every newly explored alpine district or cliff-region 
New England and eastern Canada furnishes its addition to the ab eal 
extensive list of polar and high-northern species which are 150 
south of the St. Lawrence; and to-day we know in this area, bet 
Long Island Sound and the mouth of the River St. Lawrence, 0 
than four hundred such Pteridophyta and Spermatophyta, a list-w™ 
would be significantly increased by the addition of the lower gT0¥ 
of plants. But the discovery of a few additions to this very long ' 
of arctic-alpine and high-northern plants south of the St. Lawren 
however interesting it always proves, is, in view of the extensive 
_ already amassed, only of minor importance compared with the gre™ 
= ae D. Hooker, Outlines of the Distribution of Arctic Plants: Trams. Linn. Ate 
xxiii. pt. 2, 253 (1861). See also Darwin, Origin of Species, Chap. XI; Gray, “™* 
Journ. Sei. Ser. 2, xxxiv. 144 (1862). 
