The Date-Palm (_Phoenix dactylifera_) is _the_ tree of the Desert; there only will its fruits ripen; without it, the Desert would be uninhabitable and uninhabited. Arab poesy represents it as a living being, created by God on the sixth day, at the same time as man. To express under what conditions it prospers, the imagination of the Saharan exaggerates the true, to render it the more palpable. "This king of the oasis," he says, "must plunge his feet in the water and raise his head in the fire of heaven." Science, to a certain extent, confirms this seeming hyperbole; for it needs 5100° of heat accumulated during eight months for the date to ripen its fruit perfectly. If the sum of heat be less, the fruits set, but they do not grow to their full dimensions, remain bitter to the taste, and fail in the sugar and farina, which form their nutritive properties. These conditions are realized in the climate of the Sahara. The mean temperature of the year averages from sixty-eight to seventy-six degrees, according to the locality. The heat commences in April, and does not cease until October. The thermometer seldom sinks in the cold season more than two degrees below zero, and the date can endure six degrees below zero. Rain, as already stated, is rare in the Sahara; it falls in winter, and stimulates into a newly awakened life the vegetation which has been drained of vigour by a summer sun. Sometimes they descend in torrents, but these torrents, like our summer showers, are of briefest duration. At Tongourt and Ouraegla whole years pass by without a drop of rain. Does not the reader understand, then, the gratefulness of the Arabs towards a tree which can derive its nourishment from the burning sand, the scarcely less burning airs of heaven, and the brackish waters beneath the soil which are fatal to all other kinds of vegetation--which retains its verdure fresh in the glare of a pitiless sun--which resists successfully the winds that bow to the ground its flexible stem--which provides him with beams and coverings for his tent, cordage for the harness of his horses and camels, fruit to satisfy his hunger and wine to quench his thirst--which is, moreover, "a thing of beauty," and gladsome to the eye? "Those groups of lovely date-trees bending Languidly their leaf-crowned heads, Like youthful maids, when sleep descending, Warns them to their silken beds."[70] What the vine is to the Italian, the oak to the Englishman, the cocoa-nut tree to the Polynesian, is the date-palm to the Arab. And more--far more. This single tree has peopled the Desert. A civilization, rudimentary compared with that of the West, sufficiently advanced if you contrast it with that of the Malay or the South Sea Islander, finds in it its standing-point, its centre, its support. And without it the tribes of the Sahara would cease to be.[71]