LIFE AS AFFECTED BY MAN 261 



120. Life as Affected by Man. Wherever man has es- 

 tablished himself, he has become a dominant factor in the 

 distribution and existence of plants and animals. For- 

 ests are cut down, swamps are drained and streams 

 dammed. Shade-loving plants suddenly find themselves 

 exposed to the full glare of the sun, plants which need 

 much water find themselves in a dry soil, and other plants 

 which need a dry soil are flooded by the impeded streams. 

 They cannot stand these sudden changes of environment 



ORIGINAL FLORA SUPPLANTED BY NEW PLANTS. 



and die out. The plow overturns the sod and the fields 

 are sown with seeds the natural home of which may have 

 been thousands of miles away across the sea. 



In the course of years the original flora of the region is 

 represented by only a few species inhabiting places man 

 has not deemed it worth his while to cultivate. New 

 plants suited to man's wants have taken the place of those 

 which through thousands of years of struggle have shown 

 themselves the best adapted to the geographical conditions 

 in the region. 



