84 



of these. It is also impossible to describe the exact means of 

 immigration, except in a few special cases, to be mentioned later. 



II. The Introduced Flora of the Aspexs 

 In the uncultivated aspen region, covering some ten square 

 miles on the south side of Douglas Lake and not interrupted by- 

 farms, the introduced species still occur chiefly along the road- 

 sides. Quantitative studies similar to those of 1914 were made 

 again in 1917, and the quadrats were located not only in the 

 same general region, but almost precisely in the same position. 

 In each of one hundred locations along the state road a strip of 

 2 -meter quadrats was observed, beginning at the wheel track and 

 extending at right angles to the road into the aspens until two 

 successive quadrats without introduced species were reached. In 

 the table, the figures of the first column indicate the number of first 

 quadrats (i. e., adjacent to the wheel track) in which the species 

 was observed, those of the second column the number of second 

 quadrats, and so on. 



The close dependence of the introduced species upon the im- 

 mediate proximity of the roadside is still clearly shown. Never- 

 theless, the species have extended into the aspens conspicuously 



4 s! 6 



Poa pratensis : 76 



Poa compressa 57 



Agrostis alba 42 



Phleum pratense 26 



Trifolium pratense 23 



Trifolium repens 17 



Trifolium hybridum 9 



Rumex acelosella 3 



Lepidium virginicum I 4 



Verbascum Thapsus i 1 



Achillea millefolinyn j 2\ 



Agropyron repens ■ j 



Dactylis glomerala I i ! 



Erigeron slrigosus I 



37 29I22 20 

 36 28'20 19 



9 10 II 12 13 14 '15 16 17 



4 2 

 3 I 



Total 



260 108 75 6i'62 36129 22 II 9,5 79|4 ^l-'^^ 



beyond their 1914 limits. At that time none was found more 

 than 20 meters (10 quadrats) from the roadway, while in 1917 

 they extended as far as the seventeenth quadrat, or 34 meters. 



