40 THE GEOGRAPHY OF PLANTS. 



of cold (40) is insufficient to destroy the 

 vitality of seeds. It requires a heat of 

 122. 



In proceeding to consider more definitely 

 the influence of various climates upon the 

 vegetable world, we cannot do better than 

 follow the system of baron Hmnboldt, than 

 whom no man has more successfully studied 

 this department of botanical science. He pro- 

 poses to divide each hemisphere into eight 

 zones, or bands, namely : 



1. The Equatorial Zone, from the Equator to 15 N. or s. iat. 



2. The Tropical Zone, from 15 to the Tropics. 



3. The Sub-tropical Zone, from the Tropics to 34 N. or s. Iat. 



4. The Warmer Temperate Zone, from 34 to 45 Iat. 



5. The Colder Temperate Zone, from 45<> to 58 Iat. 



6. The Sub-arctic Zone, from 58 to the Arctic or Antarctic 



Circles. 



7. The Arctic Zone, from the Arctic or Antarctic Circles to 



72 Iat. 



8. The Polar Zone, from 72 Iat. to the Pole. 



In adopting these zones, as usefully exhibit- 

 ing the influence of climate upon vegetation in 

 general, it is necessary to bear in mind two or 

 three particulars. One of these is, that it by 

 no means follows, that because two places are 

 situated on the same parallel of latitude, that 

 their temperature and climate are therefore the 

 same. Thus, though Quebec is in the latitude of 

 Paris, the country is covered with deep snow 

 four or five months in the year ; and it has 

 occurred, that a summer has passed there in 

 which not more than sixty days have been free 

 from frost. Eome, Pekin, and New York very 

 nearly agree in their latitude, but differ widely 

 both in their climates and productions. The 



