11 
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. 
“Thesoil 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. 
