nd 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, producing 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, including rats and mice, pampas-hares, and
the great nutria and carpincho (capybara) on the river banks."[9]

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 river sometimes rose 30 feet in eight hours,
doing immense destruction, and the abundance of the larger carnivora and
large reptiles on its banks, he goes on: "But it was among the flora
that the principle of natural selection was most prominently displayed.
In such a district--overrun with rodents and escaped cattle, subject to
floods that carried away whole islands of botany, and especially to
droughts that dried up the lakes and almost the river itself--no
ordinary plant could live, even on this rich and watered alluvial
debris. The only plants that escaped the cattle were such as were either
poisonous, or thorny, or resinous, or indestructibly tough. Hence we had
only a great development of solanums, talas, acacias, euphorbias, and
laurels. The buttercup is re