Page:Africa by Élisée Reclus, Volume 2.djvu/273

 FLORA. OF ALGERIA. 298 copious than ia commonly 8upi)<)secl, tho winds from every quarter being charged with some degree of moisture. But tho heaviest downpours and meet violent storms are brought by the north-west currents, which form a continuation of the fierce Provencal mistral. On the east coast tho annual rainfall varies from 24 to 60 inches, while the average, as recorded by tho observatory of Algiers for the years 1862 — 73, was found to be about 37 inches, a proportion much higher than the mean for the whole of France. But for the whole of the hill region north of the Sahara it would appear to be not more than 22 inches. On the central plateaux, which for vast spaces present no obstacle to the free play of the atmospheric currents, and where the geological structure of the soil is everywhere the same, a great uniformity of climate prevails, although the oscilla- tions of temperature between winter and summer are much greater than on the coast. In winter the cold is very severe, and vast spaces are often covered with snow, which in the depressions lies to a depth of many feet. But the summer heats, although also very intense, are more endurable, owing to the dryness of the atmosphere. Even in the Sahara, the solar radiation causes a fall of the tempera- ture during the night from 150° down to 38° F. Here also dews are abundant, but rain extremely rare, several years sometimes passing without a single shower, at least according to the reports of the natives. But their statements can now be rectified by the observations of meteorologists, who have recorded a mean rain- fall of over 3 inches at Biskra during the period from 1878 to 1883, and six times that quantity in the exceptional year 1884. Flora of Algeria. Although differing little from that of Western Tunis between Cape Bona and the frontier, the Algerian flora presents more sharply defined divisions in its several provinces, divisions due to the obstacles presented by mountain ranges and plateaux to the diffusion of plants. The greatest variety of species is found in the maritime zone and on the northern slopes of the coast ranges. Notwithstanding the destructive action of fires and a reckless system of exploitation, veritable forests still exist in this more favoured region. In the low-lying tracts and along the riverain districts, poplar, ash, and aspen trees are matted together in dense thickets by a network of creepers, while on the slopes the j)revailing species are the Halep pine, juniper, and other conifers. Thesuber, zcen (f/unrus Mirbeckii) and other varieties of the oak also cover extensive spaces, especially on the eastern seaboard. The crests of the hills are often crowned with cedars differing little from those of Lebanon, but approaching still nearer to the Cyprus variety. On the moist and wooded slopes of Tleracen the botanist Krcmer has discovered a species of poplar {jiopulm Enphratica) found elsewhere only in Marocco and on the banks of the Jordan and Euphrates. A variety of the oak also {querent castaneofolia) hitherto met only in Caucasia, is found spread over the Babor heights between La Calle and Bougie ; while other species, such as the Australian eucalyptus, have been more recently introduced by man from distant regions.