THE BISKRA REGION. 59 



abundant. Here, in fact, one passes through large thickets of Tamarix and 

 other species, and sees that the desert is much less intense than that in the 

 south, especially in the region of the M'Zab, where in many respects the 

 topography is similar. The kinds of plants also, as the list below will 

 indicate, are different in the main from those farther to the south. Where 

 the surface is most rolling we find Tamarix sp. on the heights, Zizyphus lotus 

 in the hollows, and the following grasses: Stipa tor tilts, Hordetim mariti- 

 mum, and Phalaris minor. A salsolaceous shrub (Arthrocnemon macrosta- 

 chyum) may be found in washes, Nitraria and Limoniastrum guyonianum 

 on sandy places, and Odontospermum pygmceum and Anastatica hierochun- 

 tica occur between rocks. On clay flats one finds Halocnemon strobilaceum 

 and Suceda vermiculata, indicating the presence of salts. 



The preceding notes are in part from Massart. The following species 

 are given by Doumet-Adanson as having been collected by him between 

 Biskra and Touggourt : 



Savignya longistyla. Nitraria tridentata. Nonnssa micrantha. 



Eremobium lineare. Astragalus gyzensis. Lithospermum callosum. 



Lonchophora capiomontana. Ononis serrata. Heliotropium undulatum. 



Monsonia nivea. Ammodaucus leucotrichus. Plantago ciliata. 



Erodium pulverulentum. Cyrtolepis alexandrina. P. albans. 



Fagonia sinaica. Anacyclus clavatus. Limoniastrum guyonianum. 



Haplophyllum tuberculatum. Pyrethrum fuscatum. Statice pruinosa. 



Lcefflingia hispanica. Nolletia chrysocomoides. Echinopsilon muricatus. 



Paronychia nivea. Tanacetum cinereum. Traganum nudatum. 



P. cossoniana._ Ifloga fontanesi. Ephedra alata. 



Herniaria fruticosa. Artemisia herba-alba. Cutandia memphitica. 



Zygophyllum album. Anvillaea radiata. Erythrostictus punctatus. 



Z. cornutum. Atractylis flava. Asparagus albus. 



Peganum harmala. A. prolifera. Aristida pungens. 



THE BISKRA REGION. 



TOPOGRAPHY.* 



Biskra lies immediately south of the Atlas Mountains, in the Depart- 

 ment of Constantine, 220 kilometers from the Mediterranean and about 

 400 kilometers from Ouargla. To the northeast of the oasis lie the Aur6s 

 and to the west the beginning of the Saharan Atlas, which run south of 

 west across Algeria into Morocco. Just north of the place are small hills 

 and low, jagged mountains — detached spurs from the main ranges. These 

 are the Djebel Bou Rhezal, running nearly northeast and southwest. The 

 highest of them, directly west of Biskra and about 8 kilometers distant, 

 has an altitude of 463 meters. The Bou Rhezal Mountains have a precipi- 

 tous southern face, but fall away more gradually to the north, where the 

 slope joins a wide and undulating plain. The latter extends to the base 

 of the main Atlas ranges. Southwest of the oasis, and about 2 kilometers 

 distant, a range of rocky hills extends for a distance of about 6 kilometers, 

 or until they join the mountain range of the Saharan Atlas. These hills 



* The vegetation in the vicinity of Biskra is so well known that a sketch will suffice 

 as a basis of comparison with the flora and conditions of plant life farther south. 



5 



