44 THE WORLD OF LIFE 



in no other part of the world. Passing eastward, the desert 

 regions of Baluchistan, Tibet, and Mongolia are situated 

 farther and farther north ; while abundant rainfalls and a 

 truly tropical vegetation extend far beyond the tropic into 

 what is geographically the temperate zone. This is especially 

 the case along the southern slopes of the Himalayas and their 

 extension into Burma and southern China. 



In the western hemisphere we have the desert regions of 

 Utah, Arizona, and parts of northern Mexico all in the tem- 

 perate zone. 



In the southern hemisphere the desert interior of central 

 and western Australia reproduces the Sahara on a smaller 

 scale. In Africa there is the Kalahari desert, mostly south 

 of the tropic, but on the west coast extending to about 15° 

 from the equator. In South America an arid belt of almost 

 complete desert extends along the coast from near the equator 

 to Coquimbo in Chili, whence crossing the Andes it stretches 

 south-eastward into Patagonia. Even more extraordinary is 

 the fact that in north-eastern Brazil, in the provinces of 

 Ceara, Pernambuco, and Bahia, are considerable areas which 

 have such small and uncertain rainfall as to be almost des- 

 erts, and are practically uninhabitable. And this occurs 

 only a few hundred miles beyond the great Amazonian forests 

 of Maranham in 3° S. latitude. 



With the exception of these areas of very deficient rain- 

 fall, it will, I believe, be found that the intertropical regions 

 of the globe are the most productive in species of plants, 

 and, further, that as we approach the equator, where the 

 temperature becomes more uniform throughout the whole year 

 and the amount of rain and of atmospheric moisture is also 

 more evenly distributed, the variety of the species reaches 

 a maximum. There is some evidence to show that this is 

 the case not only in the region of the great forests, but also 

 in those less humid portions which are more or less open 

 country with a vegetation of scattered trees and shrubs, to- 

 gether with herbaceous and bulbous plants which cover the 



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