188 Rhodora [SEPTEMBER 
from certain others, occupy, in a general way, wide areas in eastern 
America; and, though absent from certain localities, they may be 
said to have a far more continuous range than the alpine species, 
and the intervals between their more isolated outlying colonies are 
not too great to be crossed by seeds and spores in the ordinary processes 
of dispersal. 
The alpine plants, on the other hand, are, as already noted, present 
in our flora usually as small colonies isolated by hundreds or even 
thousands of miles from the other known members of their species. 
Dryas Drummondii, for example, one of the most abundant plants of 
the Canadian Rockies, has its nearest known colonies 2000 miles away, 
along the rivers of the Gaspé Peninsula and of Anticosti. Polystichum 
scopulinum, abundant on steep serpentine walls of Mt. Albert, Gaspé, 
is otherwise confined to mountains from Idaho to northern California, 
at least 2200 miles away. Festuca altaica, the commonest grass of 
Mt. Albert, is otherwise known only from Yukon, 2700 miles to the 
northwest, and from the mountains of Asia. Other species, though 
very isolated in their occurrence, are found at one or more points 
between our New England and Gaspé mountains and the north- 
western portion of the continent. Among such is Vaccinium ovali- 
folium whose range has been already stated. These plants, typical 
of our alpine and subalpine species, often occur, then, in such isolated 
areas that it is highly improbable that they should have reached their 
known localities by ordinary dispersal of seeds and spores from one 
of these areas directly to another. And, in view of the fact above 
pointed out, of the restriction on adjacent alpine areas of most of our 
alpine plants to prevailingly potassic, calcareous, or magnesian soils, 
it is at first difficult to see how these extremely fastidious plants could 
have grown in close association at the close of the glacial period, as 
implied by the long-accepted theory of Forbes, which was greatly 
extended by Darwin, Hooker, Gray, and others. 
When, however, we take into account the character of some excep- 
tional stations for these alpine plants at low altitudes or in less pro- 
nouncedly cliff- or rock-habitats, we get a clue to the conditions 
which they presumably found in their poleward march in the wake of 
the receding ice-sheet. Throughout New England and adjacent 
Canada and over much of the continent westward and northwestward 
there are many cold meadows and bogs or muskeags in which the 
conditions are such as to support many species which abound in alpine 
