chap, iv TROPICAL FLORAS 41 



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 

 temperate 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 Chile, whence crossing the Andes it 

 stretches south-eastward into Patagonia. Even more extra- 

 ordinary 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 

 deserts, 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 

 rainfall, 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, together with herbaceous and bulbous 

 plants which cover the ground only during the season of 

 periodical rains, as will be shown later on. 



