FROM LAGHOUAT TO GHARDAIA. 33 



Over the higher portions of the plain, one is aware that small perennials, 

 20 to 30 cm. high, are widely scattered, but it is the bare ground which gives 

 the character to the landscape. Among other forms are species of Aristida 

 and Stipa, Anabasis and Haloxylon, with dwarfed specimens of Zizyphus 

 lotus in the washes near the dayas. The leading species, Haloxylon articu- 

 latum, is much eaten by the flocks of sheep and goats (over 7,000 sheep 

 are said to obtain water at the daya), but occasionally it is present in sur- 

 prising numbers. For example, on a slope to the northeast of the daya, 

 and but a few meters distant, 227 living specimens of Haloxylon were 

 counted on an area of 16 meters square; in another place, near the crest 

 of a low hill to the west of Tilrempt, where the conditions were probably 

 as unfavorable as any in the region, 118 specimens were found on an area 

 of the same size. In both squares there appeared to be no other species 

 present. Tilrempt is said to contain 2,400 betoum trees, although the 

 visitor would not be likely to estimate the number at nearly so high a fig- 

 ure.* Numerous specimens of jujube are also scattered through the daya, 

 with some Peganum harmala and Francosuria crispa. 



As a person visits the floor of the daya he is struck by the great beauty 

 of the betoums. They are of a compact habit of growth, shapely, and cast 

 a dense shade, an unusual feature in a desert tree. Attaining a height of 

 15 meters or more, the tree may have a spread equaling or exceeding this 

 amount. The bole of the largest specimens is of large size ; one was found 

 4.56 meters in circumference, another 4 meters, while a third measured 

 3.36 meters. All measurements were made 1 meter from the surface of 

 the ground. No betoums, however, were seen to have developed in a per- 

 fectly normal way, and this observation applies not only to Tilrempt but 

 to all other dayas seen, but they were disfigured in a peculiar manner, the 

 lower branches giving the appearance of having been cut and removed at 

 a height of 2.85 meters. In fact, this had been done, and the lowest exist- 

 ing branches marked the highest point to which a browsing camel can reach. 



The leaves of the betoum are compound, consisting of 7 to 9 large leaflets. 

 The branches are unarmed and the twigs, younger branches, and leaves are 

 eagerly eaten by whatever herbivorous animals can reach them. (Fig. 12.) 

 So much is the betoum sought after as a food that it would be exterminated 

 if it were not protected by another plant, namely, the jujube.f The char- 

 acter of the leaves and young shoots of the betoum may be seen in fig. 15. 



In considering the main characteristics of the jujube we find that it is 



* Joan's Guide de l'Algerie et de la Tunisie. 



_ t 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 presente le caractere, tout a fait 

 exceptionnel, d'etre 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. 



