ii THE STRUGGLE FOR EXISTENCE 23 



paid much attention to its natural history. He says : " The 

 peculiar characteristics of these vast level plains which descend 

 from the Andes to the great river basin in unbroken monotony, 

 are the absence of rivers or water-storage, and the periodical 

 occurrence of droughts, or ' siccos,' in the summer months. 

 These conditions determine the singular character both of its 

 flora and fauna. 



" The soil is naturally fertile and favourable for the growth 

 of trees, and they grow luxuriantly wherever they are pro- 

 tected. The eucalyptus is covering large tracts wherever it 

 is enclosed, and willows, poplars, and the fig surround every 

 estancia when fenced in. 



"The open plains are covered with droves of horses 

 and cattle, and overrun by numberless wild rodents, the 

 original tenants of the pampas. During the long periods 

 of drought, which are so great a scourge to the country, these 

 animals are starved by thousands, destroying, in their efforts to 

 live, every vestige of vegetation. In one of these ' siccos,' at 

 the time of my visit, no less than 50,000 head of oxen and 

 sheep and horses perished from starvation and thirst, after tearing- 

 deep out of the soil every trace of vegetation, including the 

 wiry roots of the pampas-grass. Under such circumstances 

 the existence of an unprotected tree is impossible. The only 

 plants that hold their own, in addition to the indestructible 

 thistles, grasses, and clover, are a little herbaceous oxalis, pro- 

 ducing viviparous buds of extraordinary vitality, a few poisonous 

 species, such as the hemlock, and a few tough, thorny dwarf- 

 acacias and wiry rushes, which even a starving rat refuses. 



" Although the cattle are a modern introduction, the 

 numberless indigenous rodents must always have effectually 

 prevented the introduction of any other species of plants ; 

 large tracts are still honeycombed by the ubiquitous biscacho, 

 a gigantic rabbit ; and numerous other rodents still exist, in- 

 cluding rats and mice, pampas-hares, and the great nutria and 

 carpincho (capybara) on the river banks." 1 



Mr. Clark further remarks on the desperate struggle for 



existence which characterises the bordering fertile zones, 



where rivers and marshy plains permit a more luxuriant and 



varied vegetable and animal life. After describing how the 



1 A Visit to South America, 1878 ; also Nature, vol. xxxi. pp. 263-339. 



