10 



Minnesota Plant Life. 



part to try conclusions with those of the forest, if they obtain an 

 opportunity to penetrate between the interstices of the more 

 northern erect formation. 



Plant populations, then, in the two great vegetation regions 

 of the state, are in a state of tension, and the line between them 

 is necessarily slowly shifting and irregular. Some little change 

 in the topography, some slight modification of the drainage, 

 the drying up of a lake or the erosion of a deeper gorge by a 

 stream, may give an opportunity for one formation or the other 

 to extend its limits at the expense of its neighbor. This gen- 

 eral state of tension exists not only between the forest and the 



FIG. 3. Roadside vegetation. Grasses and pulses. An elm tree in background. 

 Cedar lake. After photograph by Williams. 



prairie, but also between plants on the tops of hills and those 

 at the base, between plants in the center of swamps and those 

 at the circumference, or between plants at the edge of a lake or 

 stream and those farther inland. 



Plant zones. The result of such competition is seen in the 

 pretty general appearance of plant zones wherever the topog- 

 raphy permits them to be developed. A simple and well-known 

 example of this tendency of plants to grow in zones or lines 

 may be seen along any road, path, ditch or trail in the state. 

 It is well known that certain kinds of plants particularly select 

 the road-side as a favorite place for growth. Such are usually 



