The part of the plain (hamada) studied lies to the west of the
oasis, between it and the adjacent hills, Mountains of the Nomads,
which are to the west of the pass of the Oued Mzi. Emerging from
the oasis, one finds himself on the arid plain, the transition
from the one to the other being abrupt. The plain, at first view,
with a covering of small stones and pebbles, gives the impression
of total barrenness. Not a tree, shrub, or herb appears to hide
the bare ground. The mountains are naked rock, while the harsh
outline of desert ranges and the distant low sand ridges give no
evidence of plant life. But a closer examination of plain, dune,
and mountains reveals the presence either of living forms or of
the dried remains of plants of a preceding moist season, in numbers
and in kinds not at first suspected.
Close to the oasis the plain forms the highway for caravans as well
as the drilling ground for army recruits, so that the herbage is
either trodden under foot or eaten to the roots. Somewhat farther
away, where the plain rises to meet the mountains, we first encounter
perennials large enough and abundant enough for consideration, the
most prominent being quedad (_Acanthyllis tragacanthoides_), adhidh
(_Zollikoferia spinosa_), rempt (_Haloxylon articulatum_), and drinn
(_Aristida pungens_); _Acanthyllis_ is perhaps the most numerous.
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.