LAKE SUPERIOR. 



I. 



THE NORTHERN VEGETATION COMPARED WITH THAT OF 

 THE JURA AND THE ALPS. 



It is now universally known that living beings, animals and plants, 

 are not scattered at random over the surface of the whole globe. 

 Their distribution, on the contrary, is regulated by particular laws 

 which give each country a peculiar aspect. We call climate the 

 physical conditions which seem to regulate this distribution, however 

 diversified the causes thus acting may be. The distribution of heat 

 all the year round ; the mode of succession of temperature, either 

 by sudden or gradual changes ; the degree of moisture of the atmos- 

 phere ; the pressure of the air ; the amount of light ; the electric 

 condition of the atmosphere ; all these and perhaps some other agents 

 continually influence the growth of plants and the development of 

 animals. The nature of the soil is no less powerful in its influence 

 upon organized beings, though here also very difierent agents are 

 considered under one head ; as the chemical properties of the ground 

 are evidently as efficient as the physical. 



Let us for a moment examine these circumstances. Temperature 

 seems to be the all-ruling power. With the returning smile of 

 spring, vegetation bursts out with new vigor, and dies again as the 

 cold of winter brings back its annihilating rigors. Under the hot 

 sun of the tropics the beauty and variety of vegetation exceed all 

 that is known in more temperate regions, whilst as we approach the 

 polar plains we see it grow gradually less diversified and more dwarf- 



10 



