The introduced vegetation in the vicinity of Douglas Lake, Michigan* 
HENRY ALLAN GLEASON AND FRANK THEODORE MCFARLAND 
Throughout the eastern states the number of introduced 
species is one of the most remarkable features of the flora. These 
plants, originating in widely separated regions, are unusually well 
fitted by their habits of growth, by their physiological demands, 
by the amount of seed which they produce, or by the nature of 
their dissemination to exist in the immediate proximity of civiliza- 
tion. An increasing density of population, up to certain limits, 
merely creates new habitats for them, extends their old ones, or 
facilitates their seed dispersal. Most of them are unable to com- 
pete with native species, except when favored by human opera- 
tions, and are not found far beyond cultivated ground. In this 
they differ radically from native plants, which rapidly decrease 
in number of species under the influence of civilization, so that 
there are in the eastern states very few species of native weeds. 
The extensive areas of unsettled land in the vicinity of the 
biological station of the University of Michigan afford a good 
Opportunity for the study of the distribution and behavior of the 
foreign species, and some of the results of this study are here 
presented. 
Douglas Lake, just south of the Straits of Mackinac, lies in a 
gently rolling country of glacial origin. Most of the land to the 
south, west, and east of the lake is sand, and formerly supported 
a4 magnificent growth of white and Norway pines. This was 
lumbered about thirty years ago and no virgin area of pine forest 
now exists in the region. The pine land has been burned over 
Tepeatedly, and is now occupied by a sparse growth of aspens, 
Populus grandidentata predominating, mixed with various other 
Species in smaller proportion. Practically none of this land is 
actually under cultivation. 
North of the lake some morainic ridges rise high above the 
ee atid ay 
* Publication no, 27 from the Biological Station of the University of Michigan. 
511 
