AND DESERTS 123 



continents, though the species differ, the general facies 

 is the same — tall grasses, thorny acacias, cactuses or 

 cactus-hke forms, and generally plants presenting 

 special features which protect them against periodical 

 drought, while allowing them to take advantage of the 

 periodic tropical downfalls. 



Of the great savana regions of the world the African 

 is especially rich in ungulates, notably in antelopes, 

 the Australian in herbivorous marsupials, notably 

 kangaroos and wallabies, while the savanas of South 

 America, a country which has witnessed an extra- 

 ordinary destruction of mammaUan types in recent 

 geological time, were relatively poor in mammaha till 

 the advent of European man. 



One of the special climatic features of the savana 

 proper is the periodic abundance of rain. As we pass 

 from the savana to the desert the dry season increases 

 in length, and the rain becomes less, and more un- 

 certain. Vegetation also gradually diminishes as the 

 conditions become less favourable, and the faima 

 becomes impoverished, the mammaUan fauna diminish- 

 ing first. In the desert proper few organisms can live, 

 but the less unfavourable regions carry a reduced 

 savana fauna, especially of insects and reptiles. The 

 Kalahari, indeed, is said to serve as a reservoir for such 

 insects as locusts, which breed there until starvation 

 forces the swarms to sweep outwards to the better 

 watered lands on the majgin of the desert. 



No hard and fast line separates savana regions from 

 steppes, this being especially true in South America, 

 where the treeless ' pampas ' op steppes of the Argentine 

 south of lat. 32° S. pass into a savana region further 

 north. It should be noted, however, that in addition 

 to the characters already given, typical savana regions 



