the floras of the different countries. Hence America is so 

 full of plants, because from the North Pole to the South* 

 high mountaineous chains, with numberless intermediate 

 branches, intersect it. Hence Canada produces different 

 plants from Pennsylvania, this again from Virginia, and this 

 again produces different from Carolina. Hence the North- 

 West coast of North America produces plants which totally 

 differ from those of the North-East coast."* 



The influence of mountains, lakes and extensive forests, 

 on the climate of a country, is well ascertained ; and since 

 we are peculiar in all these respects, our climate will of 

 course be peculiar also. But it is impracticable to give 

 a description of all the peculiarities of our climate, produc- 

 ed by local circumstances. The general prevalence of cold, 

 however must not be unnoticed. Its power on the Western 

 continent is not confined by the limits of the frigid, or the 

 temperate zone. It even mitigates, by its influence, the ex- 

 cessive heat of the torrid zone. In the same parallels of 

 latitude, on the Eastern continent, winter is scarcely felt, 

 while in America its rigor is extreme. On the contrary, the 

 sultry plains of Asia, and the burning sands of the African 

 desert, have no counterparts in America. Our summer 

 months indeed are frequently warm,t but their warmth, like 

 the cold of winter, is not lasting. \ This influence of cold on 

 the American continent, with the frequency and violence of 

 our thunder storms, and the sudden change of air after them, 

 may be the causes why we abound more in biennial and pe- 

 rennial plants, than any other part of the globe. 



It is at least the general opinion, that the weather of the 

 United States is more changeable, and less severe, than for- 

 merly ; occasioned by the diminution of forests, the drain- 

 ing of swamps, and the improvements of agriculture. If the 



* Wildenow's Botany, 8tc. page 382 the English translation. 



| In July 1812, lat. 42 1-2, Far. Thermometer stood at 96. 



t See some interesting notices on this subject in vol. 2d of Robert- 

 son's History of America, and Pinkerton's Geog. 



I am well informed that the late Dr Rittenhouse (a high author- 

 ity certainly) was decidedly opposed to this opinion. 



B 



