CHAPTER LIII 



THE VEGETATION OF NORTH AMERICA 



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Recent improvements in facilities for land and air travel have afforded 

 millions of people the opportunity of visiting most parts of the North 

 American continent. The outposts of civilization in Canada, Mexico, and 

 Central America have rather suddenly become fairly accessible to anyone 

 interested in going there. This has awakened a new interest not only in 

 unfamiliar human populations, their customs, industries, and foods, but 

 also in the native vegetation, which has always been the chief source of 

 biological supplies of isolated peoples and pioneer settlements. 



Such trips may now be even more enjovable and enlightening, for 

 enough has been learned about the biological and economic relations of 

 plants and their heredity and phvsiology that observations may be made 

 with increased understanding. Never again will plants be just something 

 green along the route, put there merely to be enjoyed, ignored, or de- 

 stroyed at will, for we know that they are the basis both of our existence 

 and of much of our individual and national wealth. The development of 

 the plants, on the other hand, is dependent upon their physical environ- 

 ment, a part of which we may alter, either to the advantage of both the 

 plants and ourselves or to the detriment of both. 



This chapter on the vegetation of North America is a brief sketch of 

 the vegetation of a continent ( Fig. 370 ) . Only a few of the many biologi- 

 cal and economic relations of this vegetation are mentioned; but many 

 others, together with interpretations of the phenomena described, can be 

 inferred from the facts presented in preceding chapters. 



The differences in climate from place to place on the larger continents 

 are so numerous that areas of similar climates and equivalent types of 

 vegetation occur on each of them. Most of the species, many of the 

 genera, and a few of the families, however, are different. 



Climatic contrasts of the continent. From north to south the greatest 

 contrasts result from differences in light and temperature conditions. 

 North America extends southward from a region of nearly continuous 

 ice and snow, where three-fourths of the year is winter and one-fourth 



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