GLEASON AND MCFARLAND: INTRODUCED VEGETATION 521 
roads, giving the species in some parts of the aspen association 
a frequency index of 2 or 3. Verbascum Thapsus occurs in scat- 
tered patches, usually grouped around a single plant of the previous 
year. The year 1914 has apparently been unusually favorable 
for this species, since many more such patches occur than ever 
before. 
The close dependence of all the introduced species upon culti- 
vation is well shown at the edge of the uncultivated area, and may 
be illustrated here by data from the margin of the aspen associa- 
tion east of Douglas Lake. A field planted to rye in 1913 stood 
idle in 1914, and was well overgrown with various species of weeds. 
It is separated by a wire fence from the uncultivated land to the 
west. A strip of fifteen 2-meter quadrats, extending from the 
fence into the field, was counted, and showed a total of 21 species. 
Of these fourteen were introduced, with an average frequency 
index of 44, and seven were native, with an average frequency of 
31. The field on the other side of the fence is well grown up with 
thickets of oak and aspen, but has been pastured and supports a 
good bluegrass sod. A similar list of quadrats showed in it sixteen 
species, of which only three were introduced, Poa pratensis, Ver- 
bascum Thapsus, and Taraxacum officinale. 
CONCLUSIONS 
I. Of 120 introduced species in the region, only 56 have been 
observed within the uncultivated region. All of these occur in 
the vicinity of dwellings; 26 along recent logging roads or camp 
grounds in the hardwood region; 21 along roads or camp grounds 
among the aspens; and only three show a tendency to establish 
themselves among the native species. 
2. The great reduction in the number of introduced species 
around the more remote settlements shows that they are in many 
cases dependent upon human aid for their dispersal. 
3. Among these 56 species are many with efficient means of 
dispersal. Their limitation to the immediate vicinity of roads, 
camp grounds, or dwellings is accordingly due, not to lack of 
mobility, but to inability to compete successfully with the native 
species, . 
