Development of the Vegetation of New York State 81 
fallen into the acceptance of such interpretations as a matter 
of course. We may forget that the layman has not had time 
or occasion — perhaps not the opportunity — to follow the 
evidence minutely, and naturally would look skeptically upon 
doctrine presented thus in general and confident conclusions. 
What I am saying at this point has of course no more perti- 
nent application to the question of the above caption than it 
has to the conclusions about the development of plant life 
in remote geologic periods, or to the doctrine as to the rela- 
tion of glacial encroachments to the plant life of that epoch, 
and the ] post-glacial migrations into the glaciated regions. 
As to the immediate question, one naturally thinks of the 
ocean barrier on the one hand and of the barrier of frigid 
climate on the other. But even aside from the rather 
abundant interchange of plants between Europe, Asia and 
America incident to ocean traffic it does not appear that 
oceanic and climatic barriers have been wholly effective 
under present conditions. Certainly the case of Diapensia 
indicates that so far at least as arctic plants are concerned, 
species of a certain aggressive individuality (whatever quali- 
ties that may involve of “ wanderungsfiahigkeit ” (possibly 
the simple matter of vigorous seed of a kind which migrating 
birds might carry) are able to disperse from their distribu- 
tion center (as seems to have been notably the case from the 
mountain lands of south eastern Asia) to the remotest habitat 
—e. g., the summit of Mt. Marcy —in the circumpolar 
regions. Engler* has repeatedly called attention to these 
migrations or dispersals over long distances of intervening 
climatic or oceanic barriers and notably i in the case of species 
distribution as between the high mountains of southern Asia 
and Europe to the summits of high mountains south of the 
equator in Africa (the Kilimanjaro district). 
1 Engler, Adolph. See papers previously cited. Also, Engler, A. 
Uber die Geographische Verbreitung der Rutaceen im Verhiiltniss zu 
ihrer systematischen Gliederung. Abhandl. d. k. preuss. Akad. d. Wiss, 
1896, and similarly the Zygophyllacee (ebenda, 1896). Bray, W. L. 
The geographical distribution of the Frankeniacee considered in con- 
nection with their systematic relationship. Engler’s Bot. Jahrb., 24: 
1898. 
