"The aspect of the Puna, or Despoblado," says Von Tschudi,[95] "is singularly monotonous and dreary. The expansive levels are scantily covered with grasses of a yellowish-brown hue, and are never enlivened by fresh-looking verdure. Here and there, at distant intervals, may be seen a few stunted Quenera trees,[96] or large patches of ground covered with the Ratanbia shrub.[97] Both are used by the Indians as fuel, and for roofing their huts. The cold climate and sterile soil are formidable impediments to agriculture. Only one plant is cultivated in these regions with any degree of success. It is the _maca_, a tuberous root grown like the potato, and, like it, used as an article of food. In many of the Puna districts it constitutes the principal sustenance of the inhabitants. It has an agreeable and somewhat sweetish flavour, and when boiled in milk it tastes like the chestnut." The most imposing spectacle presented by the Deserts of South America is that of their frequent hurricanes. As the Simoom to the Sahara, so is the Pampero to the Pampas. Its approach is foretold by signs which the native's experienced eye readily recognizes. All at once the air seems stricken motionless, and over the solitude broods a solemn silence. A cloud white and light as snow--a cloud "no bigger than a man's hand"--rises in the south-west. It advances, and as it advances enlarges its proportions. Other clouds appear, and all gather into one imposing mass. The dust rises and whirls round in thick columns suspended between heaven and earth. Lower and lower descend the congregated vapours, until they envelop the earth in a funeral shroud, whose folds the hurricane incessantly agitates, and which the forked lightnings seem to rend in fragments. Suffocating gusts of a fiery wind traverse space. And now the sudden tempest stoops down from the summit of the Andes, and sweeps the Savannah with resistless fury. Enormous masses of sand, upgathered by the _rafale_, obscure the clearness of day; at noon the earth is covered with a darkness that may be felt. The thunder mingles its roar with the strident voices of the storm. All that lives, all that breathes, is at the mercy of the unchained elements, which are as pitiless in their wrath as a roused people. Thousands of animals perish in the Savannahs; and prostrate, with his face to the earth, man tremblingly awaits the expiring breath of the grand convulsion! The horses and cattle of Europe are replaced in the Pampas of South America by the herds of guanacos and llamas which covered them at the epoch of the Spanish conquest. Their owners, descendants of the Spaniards intermingled with the native races, possess many of the characteristics of the Arab.