LAGHOUAT. 27 



by the absence of large laterals, at least near the surface. The leading 

 feature of the root-system is, in short, its tap-root. A root-system of a 

 similar type was found in Artemisia herba-alba. 



Rempt {Haloxylon articulatum) also occurs on the plain. This is a 

 shrubby perennial (half shrub?) which is possibly the most often met of 

 any species, or at least genus, in southern Algeria. It is capable of endur- 

 ing very arid conditions, is unarmed, and is much eaten by all herbivorous 

 animals. The plant will be figured and especially referred to later in this 

 study, so that at this time only a brief definition will be given of its root- 

 system, which is a typically generalized one, penetrating the ground fairly 

 deeply if the character of the soil permits, but also lying near the surface ; 

 there is also a relatively large number of secondary and tertiary roots, 

 characteristic of the generalized type.* 



Inspection of the soil showed it to be a sandy clay with a large percentage 

 of pebbles and stones and with greater depth of earth in the hollows on 

 the plain than on low ridges. It probably contains some gypsum, since an 

 outcropping of it occurs on the southern face of the low mountains to the 

 north. Taken as a whole, the soil appeared very like that of the plain by 

 Tilrempt and Ghardaia, as well as between Ghardaia and Ouargla (Gan- 

 tara) . The soil will be described later in this paper. 



THE DUNES NEAR LAGHOUAT. 



Dunes are not present in large enough numbers, or of large enough size, 

 to figure very prominently in the topography of the environs of Laghouat ; 

 but they occur both to the east and to the west of the town, those to 

 the east being the larger. Sand is found facing the south side of the 

 Rocher des Chiens, a rocky hill on the western edge of the oasis, and the 

 south side of a portion of the Nomad Mountains, to the north. There 

 is also a succession of low dunes between the Nomad Mountains and the 

 oasis. The Rocher des Chiens dune is moving from west to east, but the 

 dune along the face of the Nomad Mountains is probably stationary. 

 The series of dunes on the plain are moving toward the northeast. 



An inspection of the dunes shows that the number of individuals, as 

 well as the number of species, is very limited. In fact there are apparently 

 fewer plants here than on the dunes of large size subsequently encountered 

 between Ouargla and Touggourt. The most characteristic plant is ' ' drinn 

 (Aristida pungens), but it is by no means common; there are also a few 

 specimens of Tamarix growing near the Nomad Mountains. As fre- 

 quently happens where there are moving dunes, the passage of the dune 

 greatly changes the character of the flora. Although this feature was not 

 especially studied, it was noted that the number of grasses where the 

 dune had swept was greater than it was before this. Acanthyllis iragacan- 

 thoides, a plant typical of the plain, was found to survive the passage of the 

 sand, although changed in appearance in a characteristic manner. It will 



* Compare the root-system of H. scoparium at Biskra, p. 64. 



