About 75 kilometers from Ouargla, and on a plain similar to that just referred to, “dhamran” (Traganum nudatum) was the most common species, but was by no means abundant. The census of an area 16 by 16 meters, taken in a locality where dhamran was dominant, resulted in finding 31 living and a few dead plants, probably all Traganum. It is to be understood that the vegetation of the reg desert not far distant is much richer, not only in species but especially in individuals, and also that the plants are much larger.
From 56 kilometers to about 71 kilometers from Ouargla the route lay over more or less continuous dunes, where the leading species seen were Aristida sp., Ephedra sp., Euphorbia guyoniana, Limoniastrum guyonianum, and Traganum nudatum.
In or about the edges of the chotts, which are the leading topographical features of the region immediately south of Touggourt, the most common species are Haloxylon sp., Salsola tetragona, Limoniastrum guyonianum, and Arabis aphyla. Besides these forms, about 28 kilometers south of Touggourt fine specimens of Halocnemon strobilaceum were seen growing in an extremely salty situation, to the total exclusion of other species. Tamarix also is to be found in and about salt spots near Touggourt. (See fig. [64.])
Both Massart and Doumet-Adanson (Bull. Soc. Bot. France, 39, 1892) have discussed the flora of the Touggourt-Ouargla region. The following exhaustive list is given by the latter author as having been collected between the two desert towns:
| Henophyton deserti. | Ammodaucus leucotrichus. | Plantago ciliata. |
| Matthiola livida. | Mesembryanthemum sp. | P. psyllium. |
| Malcolmia ægyptica var. linearis. | Deverra chlorantha. | Scrophularia saharæ. |
| Moricandia cinerea. | Nolletia chrysocomoides. | Linaria fruticosa. |
| Sisymbrium pendulum. | Senecio coronopifolius. | Euphorbia guyoniana. |
| Savignya longistyla. | Anthemis monilicostata. | Atriplex dimorphostegius. |
| Reseda stricta. | Tanacetum cinereum. | Caroxylon tetragonum. |
| R. arabica. | Ifloga fontanesii. | Echinopsilon muricatus. |
| Helianthemum sessiliflorum. | Centaurea purpuracea. | Calligonum comosum. |
| H. ellipticum. | Amberboa omphalodes. | Haloxylon articulatum. |
| Randonia africana. | Rhantherium adpressum. | Anabasis articulata. |
| Frankenia pulverulenta. | Atractylis flava. | Cornulacea monocantha. |
| Silene nicoeensis. | A. prolifera. | Thymelea hirsuta. |
| Monsonia nivea. | A. microcephala. | Th. microphylla. |
| Erodium glaucophylum. | Tourneuxia variifolia. | Aristida flaccosa. |
| Fagonia glutinosa. | Catananche arenaria. | A. pungens. |
| F. frutescens. | Spitzelia saharæ. | Cyperus conglomeratus. |
| Polycarpæa fragilis. | Zollikoferia chondrilloides. | Ephedra fragilis. |
| Gymnocarpus decandrus. | Z. squamosa. | Erythrostictus punctatus. |
| Retama retam. | Scorzonera undulata. | Scilla sp. |
| Genista saharæ. | Echium humile. | Dipcadi serotinum. |
| Astragalus gumbo. | Echiochilon fruticosum. | Asphodelus pendulinus. |
| Anthyllis henoniana. | Arnebia decumbens. | Ruppia maritimus. |
| Neurada procumbens. | Statice pruinosa. | Chara fœtida. |
| Limoniastrum guyonianum. |
TOUGGOURT TO BISKRA—PHYSICAL FEATURES AND VEGETATION.
From Ouargla to Touggourt we have found that the country gradually descends, the former place being 124 meters and the latter 77 meters above the level of the sea. From Touggourt, also, for a distance of about 120 kilometers, the descent along the route continues until at the Chott Merouan a level of 6 meters is attained. The lowest places in every case are of course the chotts and the connecting oueds. The most important chott of this series is Melrirh, 11 meters or more below sea-level. This drainage system is the northern culmination of the vast one of which the Oued Igharghar is the most important part. In an earlier age water came north in the oued from the highlands of central Sahara and poured into the Chott Melrirh, having passed successively through the lesser chotts farther south. At that time, also, the Chott Melrirh probably was connected with the Gulf of Gabes.
From Touggourt to Chott Merouan, the lowest portion of the route to Biskra, the topography is that of a region of chotts; that is, there are salt spots surrounded on every side by higher ground, which in many cases is of sand. From Chott Merouan the route passes over a higher desert of a different character, which in part bears a remote resemblance to the Gantara and in part to the Ouargla plain. It is a vast plain, with little topographical diversity, which rises to meet the Atlas Mountains to the west and north. In the eastern portion it is somewhat rolling, stones are strewn plentifully on its surface (hamada), and there has been considerable erosion, so that gullies are formed. In the portion nearer Biskra the surface is more level, the soil is fine (reg), and there has been comparatively little erosion.
The soil of the chott region is largely of sand; on the hamada there is much clay, while on the reg it is fine and easily blown by the wind, and this in spite of the fact that the most vegetation seen in the Sahara was in this region. A slight breeze picks up the dust and carries it long distances in dark clouds. It fills the throat, nose, and eyes of the traveler and makes crossing the reg exceedingly disagreeable.
The plant life as seen along the portion of the route through the chott region consists almost wholly of halophytes, as would be expected, in addition to which, where for short distances the hamada or dunes were crossed, there were forms characteristic of such areas. The Tamarix is especially common in the region and Limoniastrum guyonianum is also often met.