208 PETRY: VEGETATION OF NEW YORK STATE 
Of these species, Bray, in the first paper of this series, lists three 
of the dominant ones as indicators of the Canadian zone—charac- 
teristic of the Adirondacks above 3,500 ft.—and four others as 
occurring abundantly in the Canadian Transition zone—character- 
istic of the higher Catskills and of the Adirondacks up to 3,500 ft.; 
and Cooper* lists four of the dominant species as characteristic of 
the climax forest of Isle Royale, Lake Superior. In addition, the 
manuals indicate a northern distribution for all the remaining 
species. These citations are sufficient to indicate the distinctively 
northern character of the plant association of the bottom of the 
basin. 
Without entering into a discussion of the general questions 
of discontinuous distribution, it is evident that this may be con- 
sidered to be a typical relict association, left behind at the final 
recession of the ice sheet. In this interpretation, certain condi- 
tions exist in this plunge basin which have caused or permitted 
the maintainance here of a plant association characteristic of 
more northerly regions or areas of higher altitude. That low 
temperature is the controlling factor of these conditions is the 
immediate and obvious conclusion from the data given above. 
This conclusion is strongly supported by further analysis of con- 
ditions in the basin. 
During the work in the basin it was early noticed that the 
characteristic species of the bottom association are restricted to a 
common region of limited area and irregular shape; that is, the 
conditions which caused or permitted the maintenance of the 
association in the basin exist only in a small area of its bottom. 
As already described, the conditions of soil moisture, humidity, 
wind, etc., vary but slightly within the basin and cannot be con- 
trolling factors. The growing season in the bottom area is con- 
siderably shorter than in the upper part of the basin, due to the 
late melting of accumulated snow; the frostless period is probably 
about one hundred twenty-five days—an average period for the 
Canadian-Transition zone of Bray. This short growing season 
cannot however be effective in preventing the spread of the bottom 
association up the slopes of the basin, for not only do most of the 
* Cooper, W. S. The climax forest of Isle Royale, Lake Superior, and its - 
Bot. Gaz. 55: Laas II5—140, 189-235. 1913. 
