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 frequently 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 tragacanthoides_, 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 be recalled that the species has a top consisting of several shoots, springing from the root-crown at the level of the ground, and a root-system in which the laterals and the main root are alike well developed. In order that a plant, already established, can maintain this general relation during the heaping up of the sand, the main root must grow at the crown as fast as the sand encroaches. This is exactly what happens, so that, when the dune has passed on, the shoot of the species is elevated for a space equaling the depth of the sand, which is half a meter or more. From the probability that _Acanthyllis_ is of very slow growth and that the dunes are low, it follows that the rate of dune movement must be slow. THE MOUNTAINS ABOUT LAGHOUAT. The southern spurs of the Saharan Atlas lie to the north of Laghouat, within 3 miles of the oasis. This range (the Nomad Mountains) is not over 266 meters in height. Higher mountains extend both to the west and to the east, but only the Nomads are visited. There are also two high, rocky hills on opposite edges of the oasis, the town lying between, and it is perhaps because of their presence that the water is forced to the surface, or near the surface, and the oasis is formed. The hill to the west of the town is called the Rocher des Chiens. On the south side of the Nomad Mountains is a long outcropping of gypsum; the south face of these mountains is also abrupt, carrying little soil; but on the northern face the slope is gradual and there is much soil, although rocks are abundant.