CLIMATE AND LIFE 



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312. Plant Life Determined by Climate. So completely 

 does the climate of any region control plant life, that it is usu- 

 ally with considerable difficulty that man is able to grow plants 

 in any other than their native land or one having a similar 

 climate. The character of the soil has, of course, considerable 

 influence in determining plant life, but climate is the chief 

 factor. The trained botanist can tell, practically, the climate 

 of a certain region by observing the native flora, or plant life, of 

 that region. As the climate of a certain region changes, the 



FIG. 217. Average annual rainfall map of the United States. 



flora of that region also changes. In ages past, during the 

 Glacial Period, most of central North America north of the 

 40th parallel of latitude, was covered with ice. The climate 

 then must have been similar to that of the arctic zone today. 

 The flora, or plant life, which developed as the ice sheet re- 

 treated must have been similar to that now existing in British 

 America near the arctic circle. In certain moist, cool canyons 

 as far south as Illinois and Kentucky, specimens of this northern 

 flora still linger, while the flora of the rest of the region long ago 

 changed to that typical of the temperate zone. 



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