Quedad is the most striking plant native to Laghouat. It is a shrub, related to Astragalus, usually not over 40 cm. high. A single specimen consists of a group of unbranched or little-branched stems, rather stout, of a grayish-green color, and provided with long and stout spines. As a whole the plant has a very close resemblance to small specimens of ocotillo (Fouquieria splendens) of the southwestern United States. During dry seasons the stems are bare, but when the rains return leaves are put out in the axils of the spines, which are the rachides of the leaves. The habit of quedad is shown in figs. [4] and [6.] Although the species is so well protected against attack by animals that it rarely, if ever, suffers on that account, it is made a supplemental food through the burning off of the spines. When thus prepared the half-woody stems are eaten with avidity by camels.
The census of Acanthyllis was taken on the upper portion of the arid plain at a place where the plant seemed to be most abundant. On an area 16 by 16 meters, 92 specimens were found living. This was the dominant species. Other species, present in less number, were so badly eaten by animals as to be quite unrecognizable.
The root-system of Acanthyllis offered some points of interest and a short study of it was made in the field. All of the specimens whose roots were examined were growing in the habitat above referred to and within a meter of one another. The leading results of the observation are as follows: The largest specimen studied possessed a tap-root 3 cm. in diameter at the crown. Growing rapidly smaller as it ran downward, the root gave off four laterals, of which a portion dipped at an acute angle to a depth of 20 to 30 cm., sending off branches by the way. One of the largest of the laterals was traced 75 cm. and where left was 2 cm. beneath the surface. The branches, at least of the main laterals, that is, the roots of the tertiary order, for the most of their course ran thus near the surface of the ground. One of the leading laterals was followed to the base of a neighboring specimen of quedad, where it lay close to the crown of the main root. The depth of the penetration of the tap-root of this specimen was not learned. The tap-root of a neighboring specimen ran directly downward 20 cm.; then, turning sharply, it extended in a horizontal direction for a distance of 70 cm. As the large laterals were wholly lacking on this plant, the tap-root was the entire system—surely an anomalous condition. On a third plant the tap-root penetrated the ground about 4 cm. only, after which it turned and ran the rest of its course within 4 cm. of the surface. The more superficial of the roots of a fourth specimen were found to extend to the base of the last plant mentioned. Thus it was found that the root-system of Acanthyllis, as growing naturally, extends both widely and deeply for a considerable distance, and that it is flexible to a degree; in short, is generalized[8] and closely resembles that of certain species of the Tucson region, particularly Covillea tridentata, which grows under similar conditions.
The root-systems of three or four other species were also examined. Of these Zollikoferia spinosa and Artemisia campestris were growing in a little hollow in the plain close by the habitat of Acanthyllis. Zollikoferia has a very close habit of growth with dichotomous branching (compare figs. [5] and [7]). When dry the branches are slender and of a woody hardness. The root-system of this species is characterized by a pronounced tap-root and 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 enduring 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.[9]
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 (Gantara). 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 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.