Development of the Vegetation of New York State 39 
The Glacial Period and Its Effect Upon Vegetation. 
This general review of the geological history of plant life 
has brought us down to the geologically recent Glacial epoch, 
the close of which was selected as a landmark from which 
to measure the progress of vegetation when contrasted with 
the conditions found at the beginning of exploration and 
settlement of New York by Europeans. It will perhaps 
now suffice to say that by the beginning of the Glacial epoch 
the peculiar genius of our present vegetation had already 
been gained. by that I mean its method of occupying the 
land, considering vegetation as a working organization 
engaged in its march of progress or course of development. 
More concretely, the present floristic make-up (of great 
groups, families, genera and quite largely of species) the 
present types of adaptation (growth forms), the present 
segregation into floral zones or provinces and finally the 
present types of vegetation aspects (plant societies as 
regulated by soil factors) were in existence. We have then 
to consider what effect the glacial invasion would have on 
the vegetation of the areas covered by ice, and upon the fate 
of species generally, what effect was ‘produced upon the land 
by glacial action and by the return of vegetation when the 
long period of arctic climate gave way once more to temperate 
climate. It does not affect our purpose much whether we 
consider a series of advances and retreats of the ice sheet or 
only the last one, unless we put special stress on the effects 
which these repeated experiences would have in trying out 
and fixing the qualities which our native species have come to 
possess. The consideration of details connected with the 
return and final establishment of vegetation upon this New 
York terrain are matters to be cleared up so far as may be, 
in the remaining pages of this bulletin. As preliminary we 
may assert: 
(1) That glacial invasion would destroy the vegetation 
cover of our State. 
(2) That species, if they did not already exist to the 
southward of the glacial field, would either migrate in that 
direction or be exterminated. 
