162 THE CANADIAN NATURALIST. [May 



over a wide extent of territory, and many are identical with causes 

 which produce somewhat similar results in other countries. 



There are no long ranges of mountains within the Province to 

 retard the free interspersion of its different indigenous forms, nor 

 are the Laurentide hills of such considerable height as to much 

 impede the admission of the cold boreal winds from around Hud- 

 son Bay. The great breadth of the lakes, however, must, there 

 is no doubt, preclude a migration from the northern United States 

 as extensive as under altered circumstances it would be. 



To the influences effected by our numerous and extensive lakes 

 and rivers through their currents, the formation of prairie land, 

 the evaporation from their surfaces and the necessarily modified 

 temperature of the land surrounding them, references will, in sub- 

 sequent parts of this paper, be made. 



An eminent writer on botanical as well as geological subjects, 

 thinks, that many anomalies in the distribution of Canadian vege- 

 tation can be explained by considering the chemical constitution of 

 the soil. "A little more lime or a little less alkali in the soil ren- 

 ders vast regions uninhabitable by certain species of plants. For 

 many of the plants of our Laurentide hills to extend themselves 

 over the calcareous plains south of them under any imaginable con- 

 ditions of climate is quite as far beyond the range of possibility as 

 to extend across the wide ocean."* This view is, in at least a 

 limited sense, probable. Rubus Chamcemorus Linn, and Ernpe- 

 trum nig ram Linn, have been cited as illustrations of the prefer- 

 ence maintained by some plants for soils of Laurentian origin. It 

 may be more correct to, in part, ascribe the range of these plants 

 to their known predilections for northern situations. They are 

 both in fact sub-arctic plants, and it merely happens to be a coinci- 

 dence that the Laurentian formations skirt the Lower St. Lawrence 

 and the northern shores of Lake Superior, on the coasts of the 

 former of which both of these plants occur, and on those of the 

 latter Empetrum nigrum. Were their distribution entirely depen- 

 dent upon the nature of the soil, they should occur in the country 

 around the Upper Ottawa and elsewhere, but they are not known 

 to ram-eso far to the southward. Finns Banksiand Lamb. — a less 

 northern form— and probably Polygonum cilinode Michx. would 

 seem, in our present knowledge of their distribution, to constitute 

 better illustrations of preference lor Laurentian soils and 



* Dr. Dawson ; this journal, 0. S., vol. vh, p. 'M2. 



