(3) Maximum rainfall is on the eastern slopes between 4,000 and 8,000 ft. elevation. Rainfall may be different on opposite sides of a single valley, so that the eastern walls may be grassy, the western forest-covered. It probably averages 150 in. or more, except where the slopes are protected by foot-hills. The mean annual temperature is about 72° to 75° F, with a negligible range.
(4) Constant evaporation takes place above the great Amazonian wilderness (the area of which equals half that of Europe) and this moisture is again precipitated, to be once more vaporized and con densed. With two permanent lows, one near the mouth of the Amazon, into which both north-east and south-east trades flow, and one near the boundary between Bolivia and Argentina, ex cessively high relative humidity is maintained throughout the year. It is so great that salt dissolves and matches will not ignite unless kept in air-tight boxes. Rainfall averages well over 1 oo in., with winter minimum. The mean annual temperature probably averages 78° F, with a range of 3° F.
The second flows toward the Atlantic, including such vast tribu taries of the Amazon as Maranon, Huallaga, Mantaro and Apuri mac. These clear, quick-flowing streams pass through narrow pongos (gateways) and then join the sluggish jungle streams of Amazonia, whose branches spread out over half a continent before reaching the Atlantic, nearly 3,00o miles away. The third is that of Lake Titicaca, an inland system, complete in itself, fed by per petual snow. Via the Desaguadero river, a shallow stream, it empties into Lake Aullagas (Pool*, thence into a series of salars (salt swamps) to the south, where its waters eventually evaporate.
Flora and Fauna.—The coast desert seems to be without vegetation except cacti, Furcraea and occasional clumps of gnarled algarroba trees (Prosopis juliflora), the sweet pods of which are used for cattle food. South of 8° S., however, gartias are followed by a sparse, fugitive plant cover upon the hills. It springs up as if by magic, growing more luxuriant up to about 3,00o ft., following the mists so closely that it indicates the limit
of their distribution. On the other hand, all streams are lined with vegetation—acacia, willow, pacay, pepper-trees, thorny Leguminosae, bushes and tall reeds. Where irrigation is possible there are crops and orchards including such delicious native fruits as chirimoya (Anona cherimolia), and palta (Persea gratissima).
The fauna of the coast zone is poor, consisting of rodents, armadillos, bats, scorpions, lizards and poisonous vipers in the sugar fields. There are owls, vultures and birds of prey. Otters live in some of the streams. In contrast is the teeming ocean which abounds in fish and bird life.
In the valleys of the western slopes, xerophytic vegetation may reach as high as io,000 f t. with geranium, heliotrope, floripondio, fruit trees and temperate zone crops, where irrigated. The zone of seasonal grass-steppe and small perennial plants begins at about 8,000 feet. Above 12,000 ft., the treeless puna has hard grasses, mostly ichu (Stipa jarava). Clumps of yareta (Bolax globaria) are used as fuel. On low-lying damp lands, distichia moors form a continuous carpet. Lichens and mosses and some Compositae climb to 16,000 feet. Near Lake Titicaca grows the totora (Scirpus riparius), reeds which in bundles serve to make boats for the Indians. This bleak height is the original home of the potato, oca (Oxalis tuberosa), ulluco (Ullucus tuberosus), and quinoa (Chenopodium quinoa), a grain peculiar to Peru, which heads at high altitudes, and is a staple Indian diet. Barley is the only other cereal which will head at these altitudes. In valleys there is elder, alder and Cantua buxifolia, the canto shrub of the Incas, with leathery leaves and large red flowers. There air great stands of (Polylepis racemosa), gnarled old evergreen trees 15 to 20 ft. high, and quisuar (Buddleia incana) on the valley walls, together with a fibrous plant 12 to 18 ft. high, (Pourretia gigantea), of which the prickly leaves and thorns are the bane of shepherds. If deep enough, the valley floors have xerophytic vegetation like that of coast valleys (Maranon). Tropical crops are grown in lower valleys, sugar up to about 6,000 feet.