Development of the Vegetation of New York State 85 
in the United States. The fossil forms are found in arctic 
lands of North America and Eur-Asia. 
It is of importance to observe that the floras of the eastern 
and western continents of the northern hemisphere have been 
growing less similar as one would predict as a result of isola- 
tion. This isolation grows out of the forced migration south- 
ward by polar cooling, and was of course exaggerated by the 
glacial period. Indeed, one reason ascribed for the disap- 
pearance from Europe of certain species, some of which were 
near or identical with American species, is the fact that in 
the southerly migration the Mediterrean Sea offered a barrier 
which species could not cross and so escape extermination by 
the glacial ice. 
As to the Sources of New York Flora in General. 
The impression will have been gained that when the glaci- 
ated terrain of New York and of the northeastern part of the 
continent generally was open to the return of vegetation the 
source of vegetation forming flora was the Appalachian 
region lying to the south of the terminal moraine (the 
southern margin of the ice sheet). It should also be under- 
stood, however, that species migration is taking place con- 
stantly and toward whatever terrain is open to them, environ- 
mentally speaking. Thus we have seen evidence that some 
species have come in from other continents in post glacial 
times and, admitting the category of migrations or dispersal 
by human agency, a very extensive addition has been made 
to our flora (e. g. 613 species in the vicinity of New York’). 
So more locally have there been migrations into the State 
from adjacent territory. Thus certain species of the middle 
western prairie flora appear to reach the Erie-Ontario basin 
regions. In this connection it is suggestive to recall that 
according to Hornaday ° the American bison is known to have 
entered New York along the valleys leading up from the 
southwest. Local historians believe also that the buffalo 
existed in Erie county. 
Je Taylor, Norman, Flora of the Vicinity of New York, p. 651. 
2 Hornaday, W. T. Extermination of the Buffalo, Smithsonian Report 
1887. 
