CHAPTER VIII 

 THE NEOTROPICAL REGIONS 



The distribution of the tropical vegetation of the new world 

 is very different from that in the eastern hemisphere. The whole 

 tropical region from northern Mexico to Argentina and Chile 

 is continuous, and traversed by the great western mountain range 

 of the Cordillera; and there is nothing comparable to the great 

 expanses of desert separating the African wet tropics from the 

 Indo-Malayan regions. This condition results in a much more 

 homogeneous vegetation than is found in the Palaeotropics, 

 although there is an exceedingly rich and varied flora. 



The great Cordillera traversing western America from Alaska 

 to Patagonia is a factor of the first importance in the distribution 

 of plants in western America, both within and outside the tropics. 

 This great mountain system has served as a highway for the migra- 

 tion of many plants, both north and south, and the influence of 

 this great mountain barrier on both rainfall and temperature is 

 very great, and is a controlling factor in the character of the vegeta- 

 tion within its influence. 



The area of land within the equatorial belt is very much greater 

 in America than in either Asia or Africa. While in the old world 

 the northern tropics are largely deserts, like the Sahara, Arabia 

 and northwest India, in corresponding latitudes in America the 

 land areas are of relatively limited extent, and where deserts exist, 

 they are insignificant compared with the great deserts of tropical 

 Asia and Africa. 



The equator crosses the broadest part of South America, through 

 the immense Amazon valley, with its net-work of great rivers; 

 and this whole region is occupied by the greatest continuous extent 

 of tropical forest in the world. This immense region, extending 

 from the Atlantic to the Andes is quite unequalled for the extent 

 of its equatorial forests, which for variety and luxuriance can only 

 be matched by the much less extensive forests of the equatorial 

 forest belt in West Africa and the Malayan regions. 



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