LAGHOUAT. 23 



again with an even water-line very near the crest, and presenting a singular serrated 

 appearance (the Djebel Lazareg). I counted no less than 127 little peaks rising above 

 this straight horizontal line, almost all of them of equal height, like the crests of a long 

 sea- reef ; and lower down the sides were many tidal strings, if I may so term them. Turn- 

 ing around to our left and crossing the dry channel of an evaporated and aged "Wed," 

 we had some low headlands close behind us — Ras Ainyah of the Arabs, " Prise d'eau " 

 of the French — the scene of a bloody combat under General Yusuf. Through an open- 

 ing between the mountains we debouched on a wide plain, and suddenly before us stood 

 an isolated rock. Two cliffs facing each other bore each a bastioned tower, and in a 

 depression between these lay a town. 



The town, whose situation is thus so graphically presented, is Laghouat, 

 of which the leading present interest lies in the fact that it is on the very- 

 edge of the Sahara proper. From the rocky hills by the town one can see 

 the serrated Saharan Atlas to the north, extending northeast and south- 

 west, and, turning, to the south, an expansive and gently undulating bare 

 plain, stretching without a break to the horizon. 



LAGHOUAT. 



The ancient Arab town of Laghouat, which is also an important military 

 post, is a very favorable place from which to begin a study of the plants 

 and the environment of the plants of the northern Sahara. Its altitude 

 (780 meters) is greater than that of Ghardaia (520 meters), as also that of 

 the latter place is greater than the altitude of Ouargla (150 meters). The 

 annual rainfall of Laghouat is more than that at either of the places men- 

 tioned and more dependable. The surface of the desert at Laghouat is, 

 for example, not of one type only, but characteristic of much of the Sahara; 

 that is, it is mainly stony, a hamada, but there are also sand areas, a oued 

 and its flood-plain. Finally, the plants growing in the vicinity of Laghouat 

 are largely typical of those found farther to the south, as at Ghardaia and 

 Ouargla, or even deeper in the desert. It is of great interest to observe the 

 change in the habits of the plants, in their number, distribution, and other 

 features, when one leaves a less arid region and goes toward a region of 

 gradually increasing aridity, as when passing southward from Laghouat. 



The leading plant habitats are the oasis, the arid plain, and the dunes. 

 It is not likely that any of these habitats have been greatly changed be- 

 cause of the settlement by Arabs. The arid plain and the dunes surely 

 have per se not suffered marked alteration, and the oasis itself is probably 

 not so different from what it was formerly, as the great difference in plants 

 growing in it might at first lead one to suspect. More water is brought 

 to the surface at present than in primitive times, but if it were possible 

 to remove all introduced plants, and restore all native plants peculiar to 

 the oasis, there is no apparent reason why they should not live there quite 

 as successfully as in earlier times. It does not follow that there has been 

 no modification of the flora itself, a result of the founding of a town at 

 the oasis, and it will be pointed out later that such has surely been the 

 case, but to what extent or in what way does not appear. 



