68 College of Forestry 
the element which composes the familiar maple, beech, yellow 
birch, hemlock, white pine forest. 
Also from this boreal-austral contrast point of view we 
say that the Appalachian axis makes an elevated highway 
over which boreal species — spruce, balsam, paper birch, ete., 
pass far into the southern states; that the Atlantic slope of 
this axis and the coastal plain, possessing a chmate much 
ameliorated by ocean influence, furnish a terrain over which 
austral species pass far to the north of their general conti- 
mental range. Thus, sweet gum, willow oak, southern short- 
leaf pine, persimmon and other species reach the lower New 
York region (mouth of the Hudson) and some of them extend 
up the Connecticut coast to Massachusetts, and American 
holly for example reaches the Maine coast. 
Now in the light of developmental history as we have 
briefly reviewed it and thinking especially of the status of 
vegetation centering about the Glacial epoch, I should like 
to consider this whole matter of our flora — and particularly 
of our forest flora—from a radically different point of 
view ; that is, a post glacial northward migration of the entire 
flora. We can start out in this project by expressing con- 
viction as to three pertinent matters: 
1. That before the glacial invasions, or if you please, 
before the last glacial invasion, essentially the present 
aspects of plant life as to floristic content, growth forms 
and vegetation types were present in eastern North 
America. 
2. During the period of glacial dominance, the vegeta- 
tion of the northern half of the continent was exter- 
minated. If any species were represented only in this 
glacial region they either migrated to unglaciated terri- 
tory or became extinct. 
3. After the disappearance of the ice sheet and with 
the gradual return of milder climate, vegetation reoc- 
cupied this glaciated terrain. This vegetation consisted 
essentially of the elements which had been present 
before. 
