[15]Joan’s Guide de l’Algérie et de la Tunisie.
[16]Massart, loc. cit., p. 314, suggests that the Sahara may be gradually becoming more arid and says that as a result the betoum is becoming more and more rare and may become extinct. He says “L’extinction du Pistacia atlantica présente le caractère, tout à fait exceptionnel, d’ètre uniquement l’effet du climat.” It will appear from what is said in this study regarding the effects of grazing in general, as well as the especial effects on the betoum, that if the betoum is becoming extinct the sole cause, or perhaps the main cause, is not the adverse climate.
[17]Dr. Charles Amat, Le M’Zab et les M’Zabites, p. 70, gives a somewhat higher temperature for the rocks of the southern Chebka, placing it at 90° to 100° C., or even higher.
[18]Les Oasis du Souf et du M’Zab, La Géographie, 1902.
[19]Foureau, d’Alger au Congo par le Tchad, 1902, mentions having met with indications of early settlement of the Sahara by people now forgotten, and whose tombs, inscriptions, and other remains, were well known by his Touareg servants, although not at all understood by them. So far as I have learned, however, it is not supposed that the region of the M’Zab was inhabited before the coming of the Beni M’Zabs.
[20]There are seven cities of the Beni M’Zab, of which five lie in the M’Zab Valley, close to one another. These are El Ateuf, Ben Noura, Melika, Beni Isguen, and Ghardaia. In the pre-French times these cities were bound together in a confederacy with Ghardaia as the capital. The M’Zabites are at present, and probably always have been, a peaceful trading folk. They are heterodox Moslems. In an early time they aroused the antagonism of their more warlike as well as more orthodox Arab neighbors of the Tell, who drove them away from the coast region, and again from Ouargla and other places settled by them, until safety was at last secured in the eleventh century in the “inhospitable Chebka.” Palm gardens were established which for centuries have been irrigated laboriously by very primitive methods, and the inhabitants have accumulated wealth in flocks and by barter. The relatively large population (there were 92,761 inhabitants in 1908), the really great number of domestic animals, and the great length of time which the region has been occupied, are all factors of importance in bringing about a modification in whatever way of the primitive flora.
[21]In 1908, according to the Statistique générale de l’Algérie, there were cultivated in the territory of Ghardaia 572,114 fruit trees, among which were: almond, 5,850; fig, 101,722; date palm, 209,898; other sorts of fruits, 211,761. There were also 17,268 hectares of grain under cultivation.
[22]We were informed by our Arab attendant that the kabar, particularly the fruit, made such animals as ate it insane. The spicy flavor of the plant might otherwise be distasteful to animals.
[23]Fitting (Die Wasserversorgung und die osmotischen Druckverhältnisse der Wüstenpflanzen, Zeitschr. f. Bot., 4, 209-275, 1911) states that water-storage tissue is wanting, that in addition to being large, the leaves are much divided, without trichomes, and provided with thin cuticle. The stomata are fairly large, rather numerous, and not sunk. The leaves transpire rapidly and wilt soon after being removed from the stem. The osmotic pressure of the cell-sap of the leaves was found to equal 35.3 to 64 atmospheres, from which it is assumed that this plant, like others growing under desertic conditions, has a root cell-sap of great osmotic pressure, which permits it to extract water from a fairly dry soil or at a rather rapid rate. But neither at Biskra nor elsewhere, so far as I know, does Peganum grow where the conditions are extreme, as might be concluded from the habit of the plant as given above.
[24]It has already been shown that the number of days on which rain may be expected to fall each year is greater at Laghouat than at Ouargla, and probably at Ghardaia also. According to reports, the rainy days at Laghouat vary from 20 to 84 (seven years’ observation), with an average of 49 each year. The average number of days on which rain falls at Ouargla is 14.2. The amount of rain at Laghouat is 200 mm., at Ouargla 90.2 mm. It would appear, therefore, that the average rain at Laghouat is less in amount than the average rain at Ouargla; or, in other words, it points to the torrential as being the type of the desert storm. Since, other things being equal, the greater storms would penetrate the ground the most deeply, we may here have an explanation of the emphasis at Ghardaia on the tap-root as against the generalized root as the type of the root-system.