Chapter III: Part 3

The gazelle (_Gazella dorcas_) is the leading wild animal preying upon the desert plants in the northern Sahara. It is frequently seen by the traveler to-day and was present in large numbers no longer ago than 50 years (Tristram). It is said by the Arabs to feed on the fresh shoots and leaves of many species of shrubs and trees, especially the betoum (_Pistacia atlantica_), as well as on the annual vegetation for the relatively short period when it is to be had. Other species of gazelle, according to Tristram, range farther to the south. Other herbivorous animals of the region are hares, antelope, moufflon, and bubale. The moufflon, at the time of Tristram’s visit, was “far from uncommon throughout the whole of the mountain districts, whether wooded or bare,” but the bubale, “the wildest of the wild game of North Africa,” appears not to go north of the Oued Rirh, while its home is farther south. It is impossible to know the number of wild animals subsisting on native desert vegetation, but the list given, which might be extended, suggests that it is by no means small. Although the population of wild herbivorous animals is at present considerable, it was probably much greater a few years ago, the decrease being due, as Tristram says, not so much to the greatly increased population as to the more efficient weapons used by the Arabs in hunting.[11]

Laghouat has been inhabited by the Arabs continuously for about 1,000 years, during which time the oasis and its environs have been the source of supply of all of the fuel used and for much, if not the most, of the food consumed both by the Arab and his flocks. Naturally, the food for the inhabitants of the oasis is won from the oasis itself, but that for the beasts is derived from the desert. While it is impossible to learn the number of sheep, camels, and goats which from century to century have ranged over the desert pastures, there is no reason for supposing it was not large, as at present is the case. For example, in the department of Algiers, in 1907-08, the number of sheep is reported to have been 2,109,071; of goats 1,156,500, and of camels 23,912.[12] Of these a large percentage is to be found in and to the south of the Saharan Atlas Mountains. In portions of the colony farther south, or in regions even more desertic than at Laghouat, the number of camels, sheep, and goats is surprisingly large. The statistics for 1907-08 give the population of the three classes of animals in the southern territories, that is, the territories of Ain-Sefra, Ghardaia, Touggourt, and the oases of the Sahara, as follows: sheep, 1,932,392; goats, 588,121; camels, 126,088.

The flocks of sheep and goats range at various distances from the source of their water-supply. It is quite usual for the goatherds to gather their flocks in early morning, returning to the oasis in the evening to distribute the goats to their various owners; but probably in most cases the flocks of sheep, with some goats, return to water once in two or three days, thus being able to stray from 20 to 40 kilometers into the desert. Being less dependent on water, the camels range a much greater distance. It thus appears that the area grazed over by the flocks of the Arabs is fairly circular in form, with a radius of 40 or more kilometers from the wells, and that the range of the camels may be much greater than this. It should also be noted that the caravan routes are broad tracts where all vegetation fit for fuel or food has been utilized Between the two sources of destruction referred to, the stationary and continuous and the frequent but not continuous, little territory passes untouched as a source of food-supply.

A visit to the wood markets of the town indicates to what ends the natives resort to obtain fuel. (See figs. 2 and 3.) Among many kinds of wood, some are from the oasis itself, such as the willow, plane, and palm; some from the mountains, like juniper, pine, and oak; and some from the oued, like the jujube and _Tamarix_. Much of the fuel is at present brought three days’ journey by camel. Usually the subaerial portions only of the plants are used, but in the case of the jujube both root and branches are gathered. The fuel requirements have apparently brought about the extinction of some species from certain of their earlier habitats; for example, the betoum (_Pistacia atlantica_) probably formerly either grew in the oasis of Laghouat or near by, since it was formerly in common use as a fuel. Tristram mentions the betoum, and no other species, as a source of fuel, but inquiry failed to show that at present this species is in general use for this purpose; but the betoum is a familiar sight in the region of the dayas south of Laghouat, where it is the only arboreal species of the region.

From what has been said regarding the large numbers of domestic animals that gain their entire living on the desert, it follows that of plants growing within the range of the flocks only such as are poisonous, distasteful, armed, or otherwise protected, escape partial or complete consumption. Only such species as are too small for fuel or can not be eaten by animals attain to the usual development year by year. In the vicinity of Laghouat the most prominent of the immune plants is the quedad (_Acanthyllis tragacanthoides_), which is well protected by its stout spines; and even this species is not wholly undisturbed. The jujube, also, although not common here, is provided with short spines. It is stated by Massart[13] that the camels used by him, not having eaten for five days, consumed the branches of the jujube in spite of the spines, and that _Anvillea radiata_, a composite with acrid juice, was passed by. Perhaps the plants most frequently eaten are of the genus _Haloxylon_, generally distributed from the High Plateau southward into the region of the M’Zab. That this genus is not exterminated is interesting, since it is rarely permitted to come into flower and fruit, and it appears not to reproduce to any extent, if at all, in a vegetative way.

=FROM LAGHOUAT TO GHARDAIA.=

REGION OF THE DAYAS.

From Laghouat the way lay through a gently rolling country, ever dipping to the south and southeast. No mountains relieved the monotonous horizon. “A hard stony desert alternated with rolling sandhills,” followed by a “vast level plain dotted with dayas,” to quote again from Tristram’s narrative. Somewhat to the south of Laghouat depressions are met here and there, separated from each other by the low ridges of the plain, which receive the drainage each of a limited territory. (See figs. 10 and 11.) These are dayas, and are in fact oases with an uncertain water-supply but with favorable soil conditions, so that such rain as falls on them, or is conducted to them from higher ground, sinks deeply and creates relatively favorable conditions for plants. In that the daya is the center of a drainage system, and has no visible outlet, it is comparable to the chott or salt-spot, but it is to be distinguished from the chott by the absence of salts in excessive amounts. That salts are not present in the dayas in quantity is probably due to subterranean drainage, the daya being in fact similar to the bolsons of western America. On the plain in the northern portion of the daya region the following may be observed:[14]

Echinops spinosus.
Acanthyllis tragacanthoides.
Thymelæa microphylla.
Peganum harmala.
Euphorbia guyoniana.
Citrullus colocynthis.
Artemisia herba-alba.
Artemisia campestris.
Haloxylon articulatum.
Anabasis articulata.
Teucrium polium.
Aristida obtusa.
Stipa gigantea.
Noæa spinosissima.
Asteriscus pygmæus.

In the dayas one sees _Zilla macroptera_, _Peganum harmala_, but chiefly _Zizyphus lotus_ and the betoum (_Pistacia atlantica_), which is perhaps the only species of tree outside of the oasis in this portion of the Sahara. Massart mentions not seeing any tree away from oases from the time he left Biskra until he reached the region north of Berrian, the northern portion of the Chebka. As the betoum is so conspicuous among the Saharan plants, and also from the very remarkable relationship existing between it and the jujube, the species is of very great interest. The relationship will be described under an account of one of the largest dayas of the region, that of Tilrempt.

DAYA OF TILREMPT.

The daya of Tilrempt is one of the largest (about 103 hectares) and is the most southerly of all. It lies near the southern margin of the daya region, and is surrounded by a gently undulating plain (hamada), whose surface is strewn with stones and pebbles, with apparently an underlying stratum of impervious material, since such is to be seen wherever erosions have laid it bare. The floor of the daya is free from stones, being composed of soils of a fine texture which have been washed or blown by the wind from the surrounding higher country, and is apparently not underlaid by a hardpan. Judging from the depth of the two wells at the daya (which were dug, not bored), the deeper of which is said to be 95 meters, there is an abundance of earth for the roots of the plants. Besides the wells there is a cistern, sunk below the general level of the daya floor, which receives and stores up flood-water; it is rarely filled, but occasionally contains considerable water, possibly up to one-fourth of its capacity; its filling is very uncertain, depending on the rare and scant rains. According to Massart, no rain had fallen during the two years previous to his visit, and the cistern was empty when we were there. These observations are given to show under what intensely arid conditions such a tree as the betoum (mature specimens of which carry an immense evaporating area) can become of large size, giving but slight evidence of a severe struggle against such adverse conditions. The altitude of the daya is about 600 meters.

As one crosses the plains in the vicinity of Tilrempt he notes the scantiness of the vegetation. (See fig. 9.) Here and there in the depressions are a few betoums, often only one specimen, but usually more, and in the erosion channels leading to the dayas is a sparse population of low, gray shrubs. Over the higher portions of the plain, one is aware that small perennials, 20 to 30 cm. high, are widely scattered, but it is the bare ground which gives the character to the landscape. Among other forms are species of _Aristida_ and _Stipa_, _Anabasis_ and _Haloxylon_, with dwarfed specimens of _Zizyphus lotus_ in the washes near the dayas. The leading species, _Haloxylon articulatum_, is much eaten by the flocks of sheep and goats (over 7,000 sheep are said to obtain water at the daya), but occasionally it is present in surprising numbers. For example, on a slope to the northeast of the daya, and but a few meters distant, 227 living specimens of _Haloxylon_ were counted on an area of 16 meters square; in another place, near the crest of a low hill to the west of Tilrempt, where the conditions were probably as unfavorable as any in the region, 118 specimens were found on an area of the same size. In both squares there appeared to be no other species present. Tilrempt is said to contain 2,400 betoum trees, although the visitor would not be likely to estimate the number at nearly so high a figure.[15] Numerous specimens of jujube are also scattered through the daya, with some _Peganum harmala_ and _Francœuria crispa_.

As a person visits the floor of the daya he is struck by the great beauty of the betoums. They are of a compact habit of growth, shapely, and cast a dense shade, an unusual feature in a desert tree. Attaining a height of 15 meters or more, the tree may have a spread equaling or exceeding this amount. The bole of the largest specimens is of large size; one was found 4.56 meters in circumference, another 4 meters, while a third measured 3.36 meters. All measurements were made 1 meter from the surface of the ground. No betoums, however, were seen to have developed in a perfectly normal way, and this observation applies not only to Tilrempt but to all other dayas seen, but they were disfigured in a peculiar manner, the lower branches giving the appearance of having been cut and removed at a height of 2.85 meters. In fact, this had been done, and the lowest existing branches marked the highest point to which a browsing camel can reach.

The leaves of the betoum are compound, consisting of 7 to 9 large leaflets. The branches are unarmed and the twigs, younger branches, and leaves are eagerly eaten by whatever herbivorous animals can reach them. (Fig. 12.) So much is the betoum sought after as a food that it would be exterminated if it were not protected by another plant, namely, the jujube.[16] The character of the leaves and young shoots of the betoum may be seen in fig. 15.

In considering the main characteristics of the jujube we find that it is a spreading shrub, frequently attaining a height of 3 to 4 meters, with branches well armed with stout spines. The leaves are small, simple, and leathery. (Compare fig. 14.) The spines are so efficient as a means of protection that the shrub shows no signs of being eaten by animals, although, as quoted above, Massart remarks that after his camels had gone five days without food they ate the jujube branches in spite of the spines.

The unarmed betoum and the armed jujube have a very interesting relationship, which is as follows: When the seeds of the betoum germinate the seedling is eagerly eaten by animals if it chances, as is usually the case, that the germination occurs on the open daya floor; but if the seeds are carried to a _Zizyphus_ and germinate in its midst, the young plants may attain to a considerable height before being seen by animals, and, being protected by the encircling jujube, will continue growing until they are too large to be easily killed through grazing. It usually happens that once the betoum plant appears above the top of the protecting shrub the camels attempt to reach the attractive shoots and the jujube is trodden under foot. The jujube is thus ultimately destroyed and a mound around the base of the young betoum is all of it that remains. If the jujube is relatively small and the developing betoum is discovered while still small, it will be much eaten, and probably killed; but if it reaches a considerable height before the discovery is made, only the lower branches will be devoured and the specimen will survive. Massart was unable to find any young betoums, but when my visit to Tilrempt was made, November, 1910, there were several, although so well hidden as to cause much trouble in finding them. A view of one of these is shown in fig. 13.

The betoum is eaten by the gazelle as well as by domestic animals, which are abundant enough in this region, and this fact is probably of great influence in restricting its distribution. Fairly numerous on the desert at present, according to Tristram the gazelle was very abundant in earlier times; he speaks of their tracks marking the plain like sheep-walks.

From what we have already seen regarding the ill effect of grazing, it will appear that the relation between the betoum and the jujube is a very vital one to the former; and it probably is not too much to say that the distribution of the betoum in the daya region is entirely dependent on that of the jujube, since there is no other armed shrub in the region to afford the protection essential to its survival; with relatively favorable moisture conditions, considerable depth of soil, and a protecting jujube, the betoum will flourish and reproduce now quite as well as in former years.

THE CHEBKA.

No dayas were seen after leaving Tilrempt, and the aspect of the country changed markedly and suddenly as the drainage became better defined. The hills were more abrupt and in systems, and the valleys became broad and continuous. At first the valleys were wide and shallow, the hills being low and with flat summits, but as the distance from the daya region increased, the valleys became deeper, until at Ghardaia the effect was that of low, flat-topped mountains with broad valleys between, thus remotely suggesting the topography of southern Arizona. However, in southern Algeria the mountains are not so high nor is the “mesa” (hamada) so extensive as in Arizona. The general level of the daya region is prolonged as the summits of the mountains of this the chebka region, while the valleys are eroded to a new level, that of the plain of the M’Zab. A similar condition is seen as one goes from Ghardaia to Ouargla, so that in fact there are several immense terraces, reminders of that remote period when there was more rainfall in this portion of the Sahara than at present.

Although the drainage to the south of the daya region is well developed, the valleys and mountains run in a rather confused way, so as to give to the fancifully inclined Arab the idea of a net, from which the name “chebka” is said to be derived.

The country from Tilrempt to Ghardaia is characterized by a continuously decreasing amount of vegetation. In place of the country as a whole having a covering, however sparse, as in the daya region, one is apt to consider the chebka a barren desert, absolutely devoid of plant life; but closer inspection dispels this illusion and reveals the presence, in the more favorable situations, of not a little vegetation.

In the northern portion of the chebka region one sees here and there, on the bottoms, specimens of the jujube and the betoum, as well as _Zilla macroptera_, _Retama sphærocarpa_, and _Coronilla juncea_. On the rocks at Settafa, Massart reports finding lichens, the first he had seen after leaving Biskra. However, crustaceous lichens occur on the flat tops of the low mountains by Ghardaia. Massart suggests that the absence of lichens in the Sahara (possibly they are not to be found south of Ghardaia) is because of the intense dryness and the great heat, the temperature of the rocks becoming from 60 to 70° C.[17]

At Berriane, one of the M’Zab cities, there are over 30,000 palms of a superior sort, watered from over 400 wells. The surroundings of this oasis are extremely desertic and a casual survey of the route between this place and Ghardaia, 44 kilometers distant, reveals almost no vegetation. Here the calcareous plain of Cretaceous origin, the Chebka, is even more eroded than in the portion farther to the north, and the valleys are wider. The soil is a fine clay without an admixture of sand. It is only in the most favorable places, along the washes, that plants are to be found, and here are _Deverra chlorantha_, _Anabasis articulata_, _Gymnocarpon fruticosum_, _Artemisia herba-alba_, _Ononis angustissima_, _Linaria fruticosa_, _Antirrhinum ramosissima_, and _Haloxylon articulatum_ (Massart, _loc. cit._). _Peganum harmala_ occurs very sparingly by the roadside. The habits and the habitats of certain of the above-mentioned species will be described in greater detail later in this paper.

=GHARDAIA.=

The Ghardaia region can be characterized as a vast plain, broken to the north by low, irregularly disposed mountains, and stretching for a great distance to the south and southeast with a fairly monotonous surface, diversified only by oueds, chotts, or occasional dunes, which may be the size of small mountains. Thus on the one hand one finds the fairly diversified and stony Chebka and on the other the hamada, which has been aptly described by Brunhes[18] as “le désert par excellence, la vrai désert . . . les grandes plaques pierreuses indéfinies des hamadas!”

The leading oued of this region is the M’Zab, which extends for about 270 kilometers in a direction south of east across the southern part of the Chebka. It takes its origin about 80 kilometers west of Ghardaia and extends to the vicinity of Ouargla, where it debouches on the Ouargla plain. At Ghardaia the oued lies in a valley, with abrupt sides, which is sunk about 60 meters below the surrounding plain and which at this place is about 3 kilometers in width. (See fig. 16.) There are four main tributaries of this oued, all of which join it from the north or the Chebka side. The valley of the M’Zab becomes more and more shallow as one proceeds eastward and at last lies but little below the general level of the country. Like the other deeper valleys of the Chebka, the M’Zab Valley represents the work of erosion by water at an earlier geological epoch, when the great terraces were formed. The filling of the eroded valleys has perhaps taken place during the long arid period since that time and has probably proceeded very slowly.

It appears to be uncertain how long the M’Zab has been inhabited by man, or, more accurately, by the race now dwelling there;[19] but it has probably been not less than nine centuries.[20]

At Ghardaia are several well-defined plant habitats, which may or may not be distinct topographical areas, and which differ from one another in exposure, soil conditions, and water relations. These are the plain of the Chebka (hamada), the low and flat-topped mountains resting on the plain of the Chebka, the walls of the M’Zab Valley, and the valley floor with its gardens, cemeteries, and waste lands.

The soil conditions of the areas mentioned are very diverse. On the valley walls and the mountains there are bold rock outcrops with soil in the interstices only, and here the most intensely arid conditions prevail. The soil on the hamada also is exceedingly meager. Rocks of various sizes strew the surface. It is only between them, as well as in the washes of gentle gradient, that the best soil conditions of the plain are to be found. Here a cursory examination shows a large admixture of small stones to the fine clay, the prevailing soil type, and that at a depth less than 50 cm. A white hardpan, similar in appearance to the caliche of the southwestern United States, may usually be encountered. In the drainage depressions the soil is relatively more coarse than on the more level portions of the hamada. There is also great variation in the character of the soils of the valley. Above the upper palm gardens, which are about 2 kilometers above the town of Ghardaia, will be found much sand and fairly large stationary dunes, while smaller dunes, shifted by the winds, are to be found at various places in the valley. About 10 kilometers down the valley, toward the east, the sand is blown against the valley sides, and in certain places where the walls are low it has been sifted in a thin layer over the plain itself. At the sister city of El Ateuf the drifting sand is a continuous menace to the gardens.

Between Ghardaia and the upper palm gardens, and also between this city and Beni Isguen and Melika, are bare areas, free from sand or clay, where the soil is so hard as to be used for threshing floors and where the small amount of grain grown in the valley is threshed and winnowed. The hardpan is similar in appearance to the caliche of the southwestern United States and may be essentially the same. It is of wide extent in the valley and probably underlies the largest portion of it. Near the threshing floors the upper portion of the hardpan stratum is from 2 to 3 meters above the bed of the oued M’Zab; the stratum is about 30 centimeters in thickness and is of fairly uniform structure throughout. Beneath this is another stratum, less well defined perhaps, of approximately the same thickness, and with nearly the same character, but carrying a noticeably large percentage of sand. The lower stratum is less hard than the upper one. Underneath the second stratum is soil, largely sand, containing rocks of various sizes. Where erosion of the oued banks has occurred the soft lower hardpan stratum and the yet more soft underlying soil are both removed, leaving the upper stratum projecting as a shelf, sometimes as large as 2 by 4 meters in extent. When the shelving banks break they remain practically intact, partly buried by the sandy floor of the oued. (See fig. 17.)

Along the sides of the valley, and at a distance more remote from the oued, there are occasional washed-out areas, really box cañons, where the banks show a slightly different condition of the hardpan from that just described. Here there may be three strata of hardpan. The uppermost is of the same stratum as the top stratum by the oued, and the second stratum also resembles the lower one just described. There is also a third hardpan stratum of a much different character, in that it has a very large admixture of sand and gravel, and large as well as small stones, making it more easily eroded than either of the upper strata. The soil in which the roots studied were found varied from a fine sand, with waterworn pebbles, near the oued, to a clay mixed with sand nearer the sides of the valley. In places the sand is cemented so as to resemble one of the hardpan strata above described, but it is less hard and apparently is penetrated by water without great difficulty.

The Oued M’Zab, whose channel is 15 meters more or less in width, is dry most of the year, containing water for only a few hours following the rare storms. Wells are very numerous in the valley and furnish a good supply of water. At the time of my visit to Ghardaia the water lay from 10 to 25 meters from the surface, depending on the position of the wells. The depth to water in a single well is said to vary from 1 or 2 meters to 15 meters; in other words, the water-table of the valley varies 13 to 15 meters between the dry and the moist seasons. No analysis of the water is available, but it is reputed to be noticeably saline near and below the town of Ghardaia, while above the town this quality is not apparent to the taste. The water relations of the plain are much less favorable for plants than those of the M’Zab Valley. In addition to the fact that the soil of this area receives only such water as falls directly on it, there is so little depth that the water escapes shortly after it falls, leaving only the most favorably situated soils, for example, those beneath shallowly placed rocks, or between rocks, or in deeply penetrating cracks or the depressions, with sufficient moisture for long use by plants. The depth to water on the hamada is so great that successful wells have never been dug.

THE OASIS OF GHARDAIA.

Each of the cities of the M’Zab has its palm gardens as well as gardens in which grains of various sorts and vegetables are grown. Intensive gardening is practised and the fruits of the soil, although won with great labor, are nevertheless not inconsiderable.[21]

Perhaps the most palms are to be found about 2 kilometers above Ghardaia, where they are so abundant as to form a small forest. Here, in the most thickly planted portions, one finds a veritable jungle in which the desert glare is softened by the spreading tops of the palms and by the close canopy of grape-vines which reach from one palm-stem to another. There is a second story of apricots, peaches, almonds, and figs, and on the floor one finds a variety of vegetables. Outside of the palm gardens, and adjacent to them, are the plots in which cereals are grown. These gardens are divided into diminutive fields, frequently not larger than 1 by 1.5 meters, which are separated by small irrigating ditches and smaller laterals, from which they are given water (fig. 19). Here barley, oats, and wheat are raised, and often with them are planted carrots, turnips, or other vegetables. The main ditches are rendered impermeable by heavy coats of plaster, making it possible to use with the least waste the difficultly acquired water.

THE PLAIN (HAMADA) OF GHARDAIA.

A superficial view of the plain (hamada) which lies both to the north and to the south of the M’Zab Valley does not suggest any vegetation whatever, at least during the dry season. The desert is quite as barren in appearance, as, for example, portions of the Libyan Desert are in reality. In every direction one sees grayish-brown stones and bowlders, with little earth, and in some places blackened stones, blackened by “fires from heaven” the Arabs believe, but nothing to indicate the presence of plants. Tristram has described the plain as “one mass of naked rock, rough stone, and coarse débris, from the neighboring mountain, but without a scrap of earth or a vestige of the minutest vegetation.” But close study of the plain makes out a better case than this; in fact, where the soil has accumulated in pockets, where there is a slight drainage depression, or where spaces between the rocks are filled with soil, careful examination shows the remains of annuals and not a few living perennials; but like other intense deserts, plants, even when relatively numerous, are not present in sufficient numbers and not of sufficient size to give character to the landscape or to hide the surface of the ground.

The plain on both sides of the valley was studied and a few areas carefully examined with results which are summarized in the following paragraphs.

It has already been mentioned that the walls of the M’Zab Valley at Ghardaia are precipitous, rising between 60 and 100 meters from the valley floor, their summits being the general level of the plain. Both to the north and to the south of the valley there are short but steep tributary gulches. In these gulches, and especially at the heads of the gulches, are pockets filled with earth, and here may be found some perennial vegetation. For example, at the head of such a ravine, 3 kilometers north of the valley, 10 undetermined living species were found, of which 6 were perennials and the balance were long-lived annuals or biennials. (See fig. 20.) In an analogous situation, but on the plain to the south of the valley, the aspect being similar, a larger number of plants were found, including, among other species, _Aristida_ sp., _Centaurea pubescens_, _Deverra scoparia_, _Fagonia bruguieri_, _Peganum harmala_, and _Teucrium pseudo-chamæpitys_. A census of plants was taken, where the individuals were most numerous, with the following result: On an area 16 by 16 meters there were 330 living specimens. The three dominant species were _Aristida_ sp., _Deverra scoparia_, and _Helianthemum sessiliflorum_.

On the level portions of the plain one sees almost no perennials and only the dried remains of annuals, although here and there may be found an isolated specimen of _Peganum harmala_ or even of _Citrullus colocynthis_, the latter strangely out of its proper surroundings. In one place, also, a small date palm was found surviving the extremely arid conditions. But on the hamada it is only in relatively favorable situations that plants are to be found. One such was given above and another was found on the open plain, but near the base of a low mountain, where there was a slight depression and where some water was received from the mountain run-off. The area alluded to is 10 kilometers north of the north valley wall; the south base of the nearest mountain is 100 meters to the north of the area. The ground inclines gently to the south, and rises slightly both to the east and to the west. The surface is thickly strewn with stones and the soil is clay mixed with sand, the latter predominating in the center of the depression, where there is also a relatively large proportion of small pebbles. The area studied, 16 meters square, was so selected that the depression crossed the middle portion, leaving the two sides as representing the larger part of the plain. (Fig. 21.) In a country where the conditions of plant life are so severe it is of interest to observe how slight advantages of whatever kind, such as in the square under consideration, work for the betterment of the vegetation. The dominating species was a bunch-grass, probably _Aristida_ sp., but there was also present _Haloxylon_ sp. (eaten to the surface of the ground by the passing flocks) with other undetermined forms. On the area given 414 living perennials were found with numerous dead annuals. All of the plants were growing in the depression, there being, in fact, none on the adjacent but somewhat higher parts of the hamada. The character of the soil of this square and a discussion of the root characters of plants growing in it are given in another place.

How far the paucity of plants on the plain is owing to the arid conditions obtaining there, apparently a sufficient explanation in itself, and how far to the fact that herbivorous animals, wild as well as domestic, for several centuries have been gaining their food from the plain, can not at present be well told. Observations given below, however, indicate that if areas are protected against the depredations of animals, the plants are noticeably more numerous and of a larger size than when there is no protection. This conclusion applies to portions of the plain as well as to the other habitats under discussion.

THE MOUNTAINS ABOUT GHARDAIA.

The vegetation of the low mountains and of the rocky valley walls is extremely meager, mainly on account of the small amount or total absence of soil. In certain places (for example, near Melika) the plants of the hamada descend the rocky gulch nearly to the floor of the valley, and a similar condition has already been noted at the heads of two of the larger gulches. In such places we find species of grass and _Haloxylon articulatum_ mainly, but these species are not typical of this habitat. Only two forms appear to occur on the walls of the valley or on the mountains, and nowhere else. These are the “kabar,” _Capparis spinosa_, and one or more crustaceous lichens. (See figs. 22 and 23.) The kabar is a large shrub, 1 to 2 meters high, which bears persistent and fairly large leaves. The shrub is uneaten by animals, owing to some disagreeable flavor,[22] but is provided with small spines. The species is poorly represented, there being but few individuals, and it does not exhibit exposure preference, but grows in crevices between rocks, sometimes at the base of the walls, or wherever it can attain a foothold. I have seen lichens on the flat and horizontal upper surfaces only of a ridge of low mountains about 4 kilometers north of the valley of the M’Zab; search failed to reveal any on the north surface of the mountains or on any rocks vertically placed; their position would thus subject them to the greatest temperature ranges and to the most intense aridity (fig. 26).

THE VALLEY OF THE M’ZAB.

The bottom lands, as already has been shown, are relatively favorable for plant life; here the soil is the deepest and the water relations are the best. Accordingly we should expect to find in the valley of the M’Zab more plants than we have seen on the plain, and we will not be disappointed in these expectations; but it is almost certain that in primitive times the vegetation of the valley was even richer than at present. In fact we now find in the unprotected places only such plants as are too small for fuel or are not good for food, and the useful sorts are largely wanting. In other and similar valleys, which have not been so much disturbed by man as the M’Zab and where primitive conditions still largely obtain, there is a surprising wealth of vegetation. Such conditions were seen between Ghardaia and Ouargla and will be specially noted on another page.

At present no trees occur naturally in the valley in the vicinity of Ghardaia or any of the sister cities. The French portion of Ghardaia contains ornamental or shade trees, such as the ash, sycamore, and betoum. The largest native shrubs are a species of _Tamarix_, growing by the oued, and a few specimens of _Zizyphus lotus_, the latter confined to the side gulches and numbering half a dozen specimens. Among the most generally distributed plants in the valley are _Peganum harmala_ (figs. 27 and 28) and _Haloxylon articulatum_; the former is a half-shrub of wide distribution in southern Algeria, occurring from Biskra on the north, and although not strictly confined to the flood-plains of the oued is most abundant where the soil is relatively deep. The leaves are rather large and do not appear to have unusual protection against drought.[23] Like its relative in the southwestern portion of the United States, the creosote bush (_Covillea tridentata_), it is not eaten by any animals, although not armed and not poisonous. This species, therefore, is one of the few which to-day probably retains essentially the same distribution and appearance it had before the country was inhabited. It is interesting to note that _Peganum_ is generally distributed through the M’Zab Valley, being especially abundant between Ben Isguen and Melika. Here in November _Peganum_, except where trodden under foot by the flocks and caravans, retained much of its foliage, although rain was said not to have fallen for twelve months. In the protected areas also, as will be mentioned below, this species was found to be fresh green, showing little or no indication of the long drought. Of other species found in unprotected places in the valley, _Haloxylon articulatum_ and _Henophyton deserti_, although eaten by animals so as to be recognized only with difficulty, were also fairly abundant. There were found also _Euphorbia guyoniana_, called “le bain” by our French-speaking Arab helper, because it is used by the natives as a soap, and _Nolletia chrysocomoides_, _Æluropus_ sp., and others.

PROTECTED AREAS NEAR GHARDAIA.

Of the plant habitats whose leading characteristics have been briefly given above, only the oasis and its gardens are secure against the inroads of animals. However, owing to the long settlement of the region, rather large tracts of land are at present in what must nearly approach their primitive condition. The areas referred to are the cemeteries, which, for the reason suggested, possess special interest to the botanist, showing briefly what plants might be expected to occur in the region naturally. The typical M’Zab cemetery is of varying size and surrounded by a stone wall. No plants are introduced to decorate it and no irrigation is practised within its walls. The only disturbance of the natural condition of the land is in the use for which it is set aside. The interments are so conducted that the ground appears to be always used progressively, that is, there is always an older portion and always a newer portion, and the part once used is never afterwards made use of again. From this fact, as well as others which need not be entered into, the more ancient portion of the cemeteries, after a lapse of several centuries, or even several decades, without disturbance, must be in essentially the same condition as regards the soil and water relations, which would be most affected by the fact of interment, that they were in pre-M’Zabite times.

Several cemeteries near Ghardaia and the other M’Zab towns vary greatly in their position as well as exposure; some are on the valley floor below the town of Ghardaia, and others are in side cañons; one is on the south wall of the valley with a northern exposure, and another is on the opposite wall and hence with a southern facing; one cemetery is on the edge of the plain itself. So far, therefore, as the flora of the older portions of these areas represent the ancient vegetation of the same areas, we have in them at present a means of learning something of the kinds as well as the abundance and the habits of the plants which formerly occurred here, and (by inference) of the plants which were in the region in primitive times.

Below and not far from Ghardaia, in the valley floor, is a very ancient cemetery, or rather a cemetery with a very ancient part. In the old portion the drifting sand has obliterated all traces of graves, which have long since been forgotten by the citizens of the town. In the newer portion, farther from the edge of the oued and on higher ground, the sand gives place to clay. In the older portion of the cemetery may be found a fairly rich flora and rather large plants—a striking contrast to the vegetation of the unprotected area immediately without the wall. Here one finds _Haloxylon articulatum_ and _Henophyton deserti_, both species eagerly eaten by animals, as well as _Deverra scoparia_, _Lithospermum callosum_, _Zilla macroptera_, and _Helianthemum sessiliflorum_; also grasses and other plants which I did not know. Something of the abundance and the large size of the plants is indicated in figs. 29, 31, and 32.

In one of the cemeteries situated against the south wall of the valley, but not including the wall, the conditions are somewhat different from those just sketched; the soil is a sandy loam, with rocks of various sizes in abundance, and here may be found a fairly rich flora. In the ancient portion of this cemetery the most numerous species is perhaps _Haloxylon articulatum_, also _Fagonia glutinosa_, _Fagonia bruguieri_, _Cleome arabica_, _Echinopsilon muricatus_, _Helianthemum sessiliflorum_, _Zollikoferia resediflora_, _Salsola_ sp., and others. The plants are relatively abundant and of fairly large size.

In a cemetery on the north wall of the valley, reaching from the floor to the plain above, the wall is less precipitous than at other places and there is a small amount of earth. The number of species here is very limited, being confined almost wholly to _Haloxylon articulatum_, which is fairly abundant; but in the upper portion of the cemetery are also found _Peganum harmala_ and _Capparis spinosa_.

The cemetery situated wholly on the edge of the plain has an unexpectedly large number of plants, almost all of them _Haloxylon articulatum_, which is of good size. Outside this protected area the species is neither large nor abundant, since it is eagerly sought after by camels, sheep, and goats, and a shoot no sooner appears than it is eaten to the base.

The sentiments of the residents of Ghardaia, which led to the establishment and protection of the cemeteries, made a close botanical study of them injudicious. Enough was seen, however, to establish several points, the most important being, at least for the areas considered, that there is growing in them, without irrigation, a somewhat rich flora composed of relatively large perennials. And from this fact it seems probable, if also protected against the predatory attacks of animals, that other areas under the present rainfall and other physical environmental conditions now obtaining would support a much heavier vegetation than is generally the case. How far the presence of man and of his flocks has otherwise modified the flora, especially as regards its composition, is another question, but it certainly has not been without its effect. In the portions of the M’Zab region, except certain areas rather remote from the towns, where there is no protection, the only forms which are at all abundant, or at least conspicuous, are such as are armed, poisonous or distasteful, or too small for use as fuel. Among these are _Peganum harmala_, _Zilla macroptera_, _Tamarix_, and others seen later. However, _Haloxylon articulatum_, although eaten by all animals so as never to develop in a normal manner, is surprisingly abundant, although by no means conspicuous.

ROOT-HABITS IN THE GHARDAIA REGION.

Owing to the small amount of soil, close observation of the root-systems of the plants growing on the mountains and the plain was difficult; examination of the roots in the field was therefore carried on mostly in the valley, although enough was seen of the roots of plants in the other habitats to permit a characterization of them. The roots of several species growing on the hamada close to the valley were examined with the following as the leading results: _Deverra scoparia_ was found to have a main root running directly downward 20 cm. without giving off large laterals; at that depth it forked, the resultant branches running thereafter in a horizontal direction. (See fig. 33.) _Teucrium pseudo-chamæpitys_, _Centaurea pubescens_, and _Salvia ægyptica_, all from the hamada to the north of the M’Zab Valley, have pronounced main roots. A similar type of root was seen in _Zollikoferia resedifolia_ and _Fagonia bruguieri_ from the plain to the south of the valley. Grasses growing on the plain had roots which, as usual with grasses, showed more diversity, but on the whole penetrated rather deeply. The root-system of _Haloxylon articulatum_ is of the modified generalized type, penetrating deeply also, and will be best described as an inhabitant of the valley.

From these observations it would appear that the roots of most of the plants growing on the plain have a well-developed main root, and that few, if any, perennial roots lie near the surface of the ground. This condition is rather different from that seen at Laghouat, where the root-system of typical inhabitants of a similar habitat is of the strictly generalized type and may point to a difference in some character of the habitat—for instance, the precipitation at Ghardaia.[24]

In certain portions of the floor of the M’Zab Valley the soil conditions favor full and normal development of all forms of root-systems, but in other portions, because of the presence of an impervious hardpan, such development is not possible. Where there is hardpan the presence of species with obligate tap-roots is precluded, while such as have a more flexible root-system (e.g., _Peganum harmala_) can to a degree accommodate themselves to the unfavorable soil conditions. However, one instance was seen, which will be reported below, where a plant with a tap-root was found growing on a hardpan stratum so hard as to be excavated with the greatest difficulty. The character of the root is very greatly modified by the presence of the hardpan. Following is a sketch of the root-systems of a few plants growing naturally in the valley.

_Peganum harmala_ is one of the most characteristic plants of the floor of the M’Zab Valley; so far as my observations go, it usually occurs where there is much soil and where the water relations are the most favorable. Several studies of it were carried out on plants growing in different parts of the valley. In order to make the leading study of its roots, a typical habitat was selected east of Ghardaia and nearly in the midst of the valley. Here the upper soil, to a depth of about 20 cm., is a fine sand carrying water-worn pebbles and coarse stones. Below the sand is a denser stratum a few centimeters in thickness, but not the hardpan described in another place. Below the harder stratum, to an undetermined depth, are mingled sand and gravel coarser in texture than the superficial sand.

The first specimen of _Peganum_ studied in this habitat was about 30 cm. high and in full leaf. Its roots were fibrous, that is, they were not fleshy. The root-system consisted of a main root, which ran directly downward 17 cm., and several laterals. Probably owing to the influence of the hard stratum, the main root at length turned abruptly and maintained a horizontal course for 1.5 meters. It was 1.35 cm. in diameter at the crown and 2 mm. in diameter where left, at a depth approximating 27 cm. The main root gave off a lateral 5.5 cm. from the surface of the ground, which also branched; the ultimate branches followed a fairly level course for 45 cm. At the sharp bend of the main root another branch arose and this branched in turn, the daughter branches going somewhat downward for over 43 cm. Branches from the latter roots descended to within 8 cm. of the surface. (See fig. 35.)

Differing in details, the roots of other individuals of the same species in the same habitat have on the whole a root-system essentially like the one just sketched. Even in relatively or actually deep soil the roots of this species do not penetrate deeply, but reach rather widely. They are of the generalized type,[25] similar in many ways to the root-system of _Covillea tridentata_ of the Tucson region. When growing in a habitat where hardpan comes close to the surface, the main root is not so well developed, but there is a better development of laterals than in the specimen more favorably situated as regards soil, in the habitat above alluded to.

Growing in or near the habitat of _Peganum harmala_, whose root-system has been sketched, were other species whose roots were also examined. Among these were _Haloxylon articulatum_ and _Euphorbia guyoniana_; the former is one of the native plants most eagerly sought by animals for food, for which reason it was not found possible to secure for study specimens whose shoots were entirely normal; but the plants finally chosen were the least damaged of any found outside of the protected areas. The shoot of the specimen of _Haloxylon_ examined was about 50 cm. high; its gnarled base showed that it had been subject to intermittent attacks by animals. It was found to have a main root which ran directly downward more than 30 cm.; at a depth of 10 to 15 cm. a few small laterals took their origin. (Fig. 36.) The other specimens studied showed the same type of root-system, so that _Haloxylon_ has here a well-developed main root.[26]

Growing not far from the two species whose root-systems have just been sketched, and under similar soil conditions, were several specimens of _Euphorbia guyoniana_, whose roots were also examined. This plant has a habit of growing in groups whose members are more or less widely separated. The first specimen studied was one of a colony of a half-dozen whose habit of growth is shown in fig. 38. Its shoot was about 15 cm. high and bore several narrow, smooth leaves, and was 2.5 mm. in diameter at the base. The shoot was found to go directly downward until it joined a horizontally placed fleshy root, from which the other individuals of the colony were seen to take their origin. This, apparently a root-stock, was 8 mm. in diameter and gave off two branches, 3 and 5 mm. in cross-section, which were also horizontally placed.

On the southern side of the oued, where the soil is cemented into a sort of hardpan, _E. guyoniana_ grows in greater abundance, frequently in groups but also singly. Other observations confirm those above reported, namely, that the species reproduces largely vegetatively, new plants springing from old roots, which at Ghardaia are essentially water- and food-storage organs. Only two other species were seen to have water-storage capacity, namely, _Citrullus colocynthis_, to be described directly, and _Phelypæa violacea_, which was seen at Biskra and will be described later.

In the habitat of _Peganum_, and a few meters distant, was found a specimen of _Henophyton deserti_, which had been little injured by flocks. The shoot of the plant was about 30 cm. high, and, in spite of the long dry season, was in full leaf. It possessed a long tap-root, of which 75 cm. was recovered. No laterals were given off along the portion of the root seen. Other specimens of the same species were also examined, and in every instance a similar type of root was found.

Somewhat nearer the side of the valley, but growing where there was considerable depth of sand, were several specimens of _Tamarix_, the roots of one of which were partly exposed. The plant studied was over 3 meters high and had not been injured by animals. Its root was of the tap-root type, since the main root went unbranched directly downward.

There occur in the valley a few specimens of _Citrullus colocynthis_ described by Schimper, in “Plant Geography,” as follows:

A cucurbitaceous plant resembling our cultivated pumpkin, and its long, juicy, relatively thick-foliaged and large-leaved shoots remain green throughout the summer, producing fruits as large as a child’s head. It presents, therefore, the appearance of being protected in an unusual manner against the loss of water. As a matter of fact, however, severed shoots dry up in a few minutes. The extraordinary length of the roots of colocynth alone renders its existence possible in the desert.