168 THE CANADIAN NATURALIST. [May 



Saskatchewan, but arc altogether absent from the New England 

 States, and the eastern and central parts of Canada ? Two 

 questions are, in fact, involved in considering, in the present 

 place, the distribution of the vegetation of the country surrounding 

 Lake Superior. 



The vegetation of the prairies, like that of the pampas of South 

 America and the steppes of Russia, is of a peculiar type — 

 approached, however, in general characters, by that of the marshes 

 and swamps. Leso-ucreux. Henry Engelman, and others, have 

 pointed out many of the distinctive features of the prairies and 

 their flora.* Conditions are not suitable for the extension of this 

 flora into the more eastern parts of the United States and Canada. 

 In our Erie district, however, there are a few forms which remind 

 us much of the western prairies. To these some allusion will be 

 thereafter made. 



With regard to the vegetation of the central wooded districts of 

 British America and the adjoining American States, doubtless the 

 colder climate of Lake Superior and the rugged nature of the sur- 

 rounding country preclude the eastward distribution of more of its 

 plants. Climatal and physical conditions would, besides, on prin- 

 ciples hereafter explained, encourage a different range. 



The north wesward diffusion of many American plants has been 

 referred, perhaps correctly in part, to the direction of the valleys 

 in the United States and British America. Other causes must, 

 however, be also taken into account. The principal ranges of 

 North American mountains have a general northern and southern 

 course, with considerable inclinations to either the eastward or 

 westward. The prevalent trends are in fact parallel with the 

 coast lines of the continent. The directions of the large rivers, 

 again, are generally north-east, south-east, or nearly south-west. 

 Here we have furnished to us as the general course of the valleys, 

 along which the southern temperate flora may with facility migrate, 

 two directions — one to the north-east, and the other to the north- 

 west. Still further, the central parts of the continent are com- 

 paratively low lying, not exceeding at the headwaters of the Mis- 

 sissippi 1700 feet above the ocean; and the watershed, which 

 separates the rivers which flow into the great lakes and the St. 

 Lawrence from the tributaries and subtributaries of the Missis- 

 sippi, crosses the northern part of the State of Wisconsin, and 



* Amor. Journal of Science [2] xxxvi. 384 ; id., xxxix. 317. 



