Arctic flora and glacial Plants. 181 
plants in the circumpolar regions was by no means difficult, It is probable 
that in Scandinavia, Iceland, Greenland and North America many of the old 
glacial plants survived in the far north during the glacial period and that, 
therefore, the arctic region still contains endemic forms which have always 
been peculiar to it, such as, Dupontia Fischeri and Pleuropogon Sabini. The 
herd of glacial plants moved south from the far north into each one of the 
continental masses, America, Europe and Asia, where they were subjected to 
vieissitudes of climate to exposure to greater amounts of sunlight, where the 
physiographic and edaphic conditions were of great variety consisting of 
mountains, plains, valleys, sand hills, rock exposures, mud flats, bogs, moors 
and tundra. The outcome of such exposure to widely diverse conditions 
brought about a great differentiation of form and new species arose by muta- 
tion’). Space will not permit a differential exposition of the influences brought 
to bear upon the glacial flora along the southern edge of the great ice sheet. 
Where the vicissitudes were greatest and the edaphic and physiographic con- 
ditions nearly uniform, we find comparatively little differentiation of new types. 
The sparseness of the flora of the eastern United States, except Mount 
Washington and one or two other localities, in glacial plants is thus accounted 
for. The effect of the glaciation on the eastern United States was much more 
severe than in the western, because the mountains were lower and practically 
with the exception of Mount Washington and perhaps Mount Katahdin covered 
with the continental ice cap. The absence of true glacial plants on any 
of Alleghany mountain tops, or ranges, is accounted for by the fact that 
these mountains were not sufficiently high to support any local valley glaciers 
and because, as we will see in a short time in what follows, they were covered 
by dense vegetation which represented a relict of the great Miocene flora which 
previously covered the continent. — In the Rocky Mountains and on the 
Sierra Nevada Mountains of the western United’States, the climatic con- 
ditions were such during the period of extreme glaciation as to encourage the 
differentiation of species by mutation, for the upper valleys of these ranges 
supported local glaciers and their summits were sufficientiy high and the ex- 
posure to light and the edaphic conditions so diverse, as to supplement to an 
important extent the action of the climatic surroundings. We find in the Rocky 
Mountains, as we shall enumerate later, a comparatively rich glacier flora 
which persists today in many ranges, such 'as the Selkirks, and on such peaks 
as mounts Rainier, Shasta, Baker and Hood. With the retreat of the great 
continental ice sheet, the original arctic flora fled in part back to the arctic 
regions augmented by the new forms, which had been evolved during the 
glacial period on the mountains and along the southern limits of the ice sheet. 
As we will see shortliy, many plants remained in the north on the nunataks 
1) Contrast the views of G. R. WIELAND in a paper entitled Polar Climate in Time the major 
Factor in the Evolution of Plants and Animals. American Journal Science XVI: 401-430 
Dec. 1903. 
