+--------------+----------+--------+-------+----------+
| Station. | January. | April. | July. | October. |
+--------------+----------+--------+-------+----------+
| | _°C._ | _°C._ | _°C._ | _°C._ |
| Laghouat | 439 | 476 | 1,135 | 668 |
| In Salah | 641 | 1,027 | 1,455 | 1,121 |
| Ouargla | 570 | 909 | 1,444 | 923 |
| Ft. National | 230 | 470 | 697 | 564 |
+--------------+----------+--------+-------+----------+
The variation in total heat received at the three desert stations
may probably be explained partly at least by their differences in
latitude and in elevation above the sea, as well as the different
relations they hold to the highlands of the northern portion of
the colony. Laghouat lies immediately south of the Saharan Atlas,
latitude 33°48′, and at an elevation of 780 meters. Ouargla is
approximately 200 miles south of the mountains, latitude 31°55′,
and altitude 150 meters. In Salah is in the midst of the western
Sahara, latitude 27°17′, and about 300 meters above the sea. Fort
National lies in the Tell about 30 miles from the sea, and at an
altitude of 916.3 meters. The latitude of Fort National is 36°38′.
There are no published records of the soil temperatures of southern
Algeria. In the following table is given soil-temperature data
taken at Ghardaia by M. Buret. Maximum and minimum standard chemical
thermometers were used. They were placed in a horizontal position
in fixed tubes which were about 30 cm. in length. Precautions were
taken to properly insolate the instruments. The depth was 15 cm.
TABLE 12.—_Soil and air temperatures, Ghardaia, July_ 2-11, 1911.
+---------+---------------------+---------------------+
| | Soil. | Air. |
| Date. +----------+----------+----------+----------+
| | Maximum. | Minimum. | Maximum. | Minimum. |
+---------+----------+----------+----------+----------+
| | _°C._ | _°C._ | _°C._ | _°C._ |
| July 2 | 36.0 | 31.0 | 41.0 | 21.0 |
| July 3 | 36.0 | 31.0 | 41.0 | 22.0 |
| July 4 | 36.0 | 31.0 | 41.0 | 23.0 |
| July 5 | 36.5 | 31.5 | 41.0 | 23.5 |
| July 6 | 33.7 | 32.0 | 41.0 | 25.0 |
| July 7 | 36.0 | 32.5 | 40.0 | 26.0 |
| July 8 | 36.0 | 32.5 | 38.0 | 26.5 |
| July 9 | 37.0 | | | 25.0 |
| July 10 | 37.0 | 32.5 | 40.0 | 24.0 |
| July 11 | | 33.0 | | 23.0 |
+---------+----------+----------+----------+----------+
An examination of the meteorological reports for Algeria shows
that the direction of the prevailing winds varies considerably,
although the variation is possibly greater near the coast than in
the interior. The winds undoubtedly play an important rôle in the
environment of the vegetation of the country. At Algiers, in 1907,
winds were reported from the north 288 times, from the east 203
times, from the west 224 times, and from the south 51 times. At
Barika, on the High Plateau, the number of times and the directions
of the winds for the same year are as follows: northeast, 203
times; east 242; south 21, west 89, and southwest 93. At El Golea,
on the desert, the winds were as follows: north 192, northeast 614,
southeast 107. The winds from the north, or northerly winds, are cool
and laden with moisture, but they are most effective in regions near
the coast or in the mountains. Winds from the south are dry winds,
and are probably of great importance in limiting the distribution
of plants through the increased aridity caused by them.
The most important of these desert winds is the sirocco, a wind that
is most likely to blow in spring and summer, although occurring in
autumn also, and to a very limited degree in the winter season. The
sirocco crosses the Mediterranean and is felt in the southern
portions of France, on the Italian Riviera, and in other parts of
southern Europe. It is especially common on the High Plateau; for
example, during five years it was reported on an average of 28.4
days each year. It does not generally last more than three days,
but at Batna, in July, 1902, it was recorded on eight consecutive
days. The sirocco operates to lower the relative humidity and
to raise the temperature. For instance, on the first day of the
eight-day sirocco above alluded to, the average relative humidity
was 16 per cent, while the average on the preceding day was 25.6
per cent. It has already been remarked that on the days of the
greatest temperature variation the sirocco was usually blowing. In
the desert the winds often bring with them much dust and sometimes
last during several days; for example, one is reported at In Salah,
in May, 1904, for six consecutive days. Such winds on the desert may
come from the north, or at least may be northerly, and when storms
of this character are in progress, although possibly destructive of
animal life or at least comfort, the effects as regards decreasing
the relative humidity and raising the air temperature are not so
marked as is the case when the sirocco is blowing.
=SOME CHARACTERISTICS OF THE VEGETATION OF THE TELL.=
Because of the similarity in the flora of Algeria and southern
Europe, a very good introduction to Algeria is by the way of southern
Spain, France, or Italy. As one approaches southern France, for
instance, he begins to see evidences of increasing aridity. Upon
passing Lyons grassy fields and heavy forests are left behind, the
hills become bare or covered with a chaparral-like growth, and the
practice of irrigation is observed on the plains. The vegetation,
especially of the region between Avignon and Nimes, recalls that
of portions of California, and one sees the mulberry, the olive,
and the pomegranate in abundance, and occasionally the orange. Very
much the same conditions greet one when he arrives in Algiers, except
that along the littoral, at and in the vicinity of Algiers, there is
a wealth of native and especially of introduced plants, which give
little hint of the arid regions close at hand. The hills which make
a part of the beautiful city of Algiers contain fine plantations
of foreign trees, such as eucalyptus, conifers of various species,
acacias, figs, and a variety of fruit trees like the apricot, peach,
plum, apple, almond, orange, and others. In the fine public squares
one sees large palms also, and in the botanical garden are bamboos,
palms, bananas, India-rubber trees, and a large number of forms from
the subtropics. The great variety of introduced plants which appear
to thrive on the littoral again recalls portions of California,
where the kinds and numbers of introduced plants which grow well are
likewise large, and where the floral strangers are gathered from
the antipodes. But among the species there are also many natives
to the colony and which one will see when he begins to travel away
from the coast; for example, the cedar from the higher mountains
(_Cedrus atlantica_) and the fine pine (_Pinus halepensis_) from
lower altitudes; there are junipers and oaks, among the latter
the cork oak (_Quercus suber_), and fine specimens of _Pistacia
atlantica_ and its protector the jujube (_Zizyphus lotus_), the
relationship of which will be given later in this paper. Both of
the last-named species are native to the Sahara and are of rather
frequent occurrence in the regions visited.
Upon leaving Algiers one soon encounters a striking change in the
character of the vegetation, evidences of a rather small rainfall
and a low humidity, and one appreciates the fact that even near the
coast the climate of the colony is fairly arid. A fine general view
of the region about Algiers, giving at a glance its setting and
these features, is to be had from the heights behind the city. In
the words of Tristram (The Great Sahara):
Here we turned to observe the magnificent panorama of the city and
the harbour below, with the bay stretching far beyond, the slopes
of Mustapha on the right studded with villas, the Sahel range
terminating beyond the massive tower of the seminary of Kouba,
the conspicuous Maison Carée . . . planted where the plain of the
Metidjeh opens to the sea, the range of the lesser Atlas in the
distance beyond, and the peaks of the Djudjura, the last stronghold
of the Kabyles, behind them, capped with snow.
Crossing the plain of the Mitidja (Metidjeh), the route runs
through a country devoted largely to the raising of wine grapes,
with bare hillsides, or hills covered with low shrubs and small
trees, and, following a custom derived from France, with either side
of the highway lined with trees, mulberry and ash. At the base of
the Atlas we see large orange-groves and numerous fig trees. The
lower slopes of the mountains are covered with a chaparral-like
growth, and as one penetrates the mountains, ascending gradually
alongside the Oued Chiffa, he sees, among other forms, extensive
areas of dwarf palm, doum (_Chamærops humilis_), which resembles
remotely the familiar saw-palmetto of the southern portion of the
United States. The leaves of the doum are gathered by the Arabs for
making into baskets, rope and other useful articles, and several
donkeys laden with doum bales were observed being vigorously driven
marketward by their small bournoused masters. On the sides of the
gorge one sees species of delicate ferns, bunch-grass in tumbling
masses (very luxuriant where there is moisture), chestnut, arbutus,
and masses of evergreen ivy overhanging the way in places. At one
place, fairly high in the mountains, a colony of native monkeys has
found a safe retreat and may be frequently seen gamboling among the
rocks and the shrubs near the stream. They were seen and described
by Tristram about 50 years ago, who states that they “are of the
same species as those of the rock of Gibraltar.” Here are a few
oaks, myrtles, some “dherou” (_Pistacia_ sp.), and a few and
scattering specimens of _Pinus halepensis_. The upper portion of the
mountain, at least of the part seen, is nearly treeless, and is under
some cultivation. After leaving the pass a drive of a few minutes
brought us to the old Roman town of Medea, which appears from the
character of the vegetation, both native and introduced, to have
a cooler as well as drier climate than Algiers. Conspicuous among
the ornamentals are the Judas tree and the plane, both planted much
about the town; among the fruits the apple is cultivated extensively.
From Medea to Berrouaghia the mountain range is broken up into large
rounded hills, in part cultivated, but almost wholly open, scantily
covered with shrubs or trees and mainly grazed over by large flocks
of sheep and goats. About midway between the two places we pass
through an open forest of oaks, from whose boles the bark has been
removed. A chance acquaintance told us that the cork was removed
about once in four years, but this is probably not the true cork
oak (_Quercus suber_), which grows under more moist conditions,
as between Tunis and Constantine, or between the latter place and
Algiers, along the littoral. The altitude of this region is somewhat
under 4,000 feet.
From Berrouaghia to Boghari, which is on the northern edge of the
High Plateau, the route runs through an open grazing country,
with scattering oaks (_Quercus ballota_), juniper (_Juniperus
oxycedrus_), and “dherou” (_Pistacia lentiscus_), and, among
other herbaceous plants, not a little bunch-grass, whose species I
did not learn. On the northern slopes of Mount Gorno, 3,500 feet, is
an open forest of oak of the species named, the formation recalling
the chaparral of California. Upon reaching the crest of the mountain
one is suddenly brought to a forest of pine (_Pinus halepensis_)
which covers the entire southern slope to the exclusion of other
species of trees. Spreading over the slope on the upper levels, it
avoids the gulches near the base and reaches out on the crests of
the ridges for a considerable distance. The width of forest where
crossed is about 50 kilometers. In its habitat, which comprises the
lower Atlas Mountains, _Pinus halepensis_ forms a rather small tree,
shapely, with rounded summit. When growing somewhat apart from its
fellows it is of a more squat appearance than when in the forest,
although the forest of the species is by no means a dense one.
=THE FORESTS OF ALGERIA.=
There are estimated to be between 5,000,000 and 8,000,000 acres
of forested land in Algeria. Although the forests lie mainly
in the Tell, certain species, notably _Pinus halepensis_, occur
in the Saharan Atlas as well. Trees also grow along the oueds,
especially on the High Plateau, but not in sufficient abundance
to constitute forests proper. The leading species are, among the
conifers, _Cedrus atlantica_ and _Pinus halepensis_. The junipers
are of importance mainly as a fuel, but do not form forests. Three
oaks, namely, _Quercus ballota_, _Q. suber_, and _Q. lusitanica_,
are forest-making species, but several other common forms, such
as the olive, the plane, the ash, and the betoum (_Pistacia_),
may share in the making of a mixed forest, but do not occur in
sufficiently large numbers each to constitute a forest. In 1908
in the civil domain the acreage of the leading kinds of forest
trees was as follows: oak, 1,853,520; pine (_Pinus halepensis_),
1,398,470; juniper (about one-half being _Juniperus communis_),
444,780; and _Cedrus atlantica_, 85,000.
The species of trees are distributed in well-defined zones,
because of which they may to a large degree be segregated, or
at least the specific composition of the forest, if a mixed one,
may be determined. In altitudinal range, the oaks are found from
sea-level to 6,000 feet, within which each species may have its
characteristic range. For example, _Quercus suber_ reaches from
sea-level to 2,500 feet; _Q. ballota_ from 2,500 to 4,000 feet;
and _Q. lusitanica_ from 3,500 to 6,000 feet. _Pinus halepensis_
grows from the sea-level to 3,600 feet, and probably much higher
in the Saharan Atlas, while _Cedrus atlantica_ is to be found from
4,000 to 6,000 feet. _Abies barborensis_ is said to attain a higher
altitude than the cedar.
Among the definitive physical factors by which the composition of a
forest is determined—the rainfall, the temperature, the soil, and
the altitude—probably of the first rank should be considered the
rainfall and the temperature, which are affected by the altitude. In
the case of the distribution of the cork oak, however, the character
of the soil plays an important rôle. This species grows only on
sandy soil, and where the rainfall exceeds 600 mm. Because of the
latter requirement the larger part of the cork-oak forested area
is east of Algiers, the annual rainfall to the west of that place
falling for the most part under 600 mm. Similarly the minor features
of distribution, inside of the specific range, may be explained. For
example, in the upper limits of its range, _Pinus halepensis_
appears chiefly on southern slopes, as on Mount Gorno, while at the
low altitudes it is to be found on the northern face; temperature
reactions apparently—familiar phenomena in mountainous districts.
Because of the unison of response to common environmental factors,
much of the forested area, especially at the higher altitudes, is
composed of one species or one species largely predominates. This is
true of the pine and the cedar forests to a marked degree; _e.g._,
in the pine forests on Mount Gorno and the cedar near Batna.
Commercially speaking, the cork oak is at present the most important
species in Algeria. It occupies about 600,000 acres, and the yearly
yield is valued at nearly $1,000,000. It may be seen along the
railroad between Tunis and Constantine and east of Algiers. When
old the species has a peculiarly gnarled appearance, with a short,
stout bole, usually hollow, which may become 10 feet in diameter,
with irregular, straggling branches. It is less symmetrical in nature
than under cultivation, as in the Santa Clara Valley and Santa
Barbara, California, where a few specimens may be found. Another
species of oak, _Quercus ballota_, of no great commercial importance,
provides the source of the acorns in general use among the natives
for food. The acorns are found in all markets, even (as in Ouargla
and Ghardaia) where transportation for considerable distance
is necessary; they are less astringent and hence more pleasant
than those of most species. Although _Q. ballota_ appears not to
be planted for its fruit, it has been stated (Kearney and Means,
_loc. cit._) that the Kabyles preserve such selected trees as have
superior fruit, which would perpetuate the best-liked varieties. It
may be remarked in passing that the seeds of the pine are also
in common use among the Arabs as a food, although not employed so
generally nor in so many ways as the acorn.
The cedar (_Cedrus atlantica_), the most beautiful tree in Algeria,
is found in high altitudes only and on mountains separated from
one another, but always in the more northern Atlas ranges. In the
following mountain groups are to be found the main cedar forests,
namely: Ouarensis, Teniet, Blida, Babor, Maadid, and the Aurés. The
forest seen was that near Batna, near the western base of the most
important range in Algeria, the Aurés. Somewhat below the lower
limit of the Batna cedar forest is an open forest of oaks (_Quercus
mirbeckii_), _Juniperus oxycedrus_, and _J. phœnicea_, mingled with
which are shrubs suggesting those of the desert, such as _Acanthyllis
numidica_ and _Retama sphærocarpa_, as each genus is represented
south of the Saharan Atlas on the open desert. These species are
mainly confined to the southern facing, and hence on the side of
the mountains opposite the beginning of the cedar. By the roadside
are to be seen also several specimens of _Juniperus oxycedrus_
badly infested with the mistletoe (_Arceuthobium oxycedri_). In
one instance the unusual condition was observed of a mistletoe
group remaining alive on a host branch which appeared to be dead
for several inches below the point of attachment.
The first representatives of the cedar forest were encountered as
stragglers in the dry wash at the north base of the mountain on
which the forest is situated. In part these trees were shapely, with
a taper summit, and in part they were short, with a summit broad
and flat, in effect like an inverted cone. When the main forest
was entered the trees were mainly of the type first characterized,
with widely reaching lower branches and slender summits. In exposed
places or in older parts of the forest the trees of the second type
were often seen; and on the crest of the mountain the most bizarre
shapes (induced by wind action), the trunks nearly parallel to the
ground and the branches hugging the ground. In the upper portion of
the forest the trees were more widely separated than in the lower
portion, and here and there we met with really large specimens, which
must have been very ancient. One of the large trees had a bole which
1 meter above the ground was about 5 meters in circumference. The
trees were fruiting freely, but we did not see many seedlings. Why,
was not apparent. There were no indications that fires had swept
over the mountain recently.
=THE HIGH PLATEAU.=
The vegetation of the High Plateau, taken as a whole, is sparse, due
in part to rather light annual precipitation, but largely to the lack
of efficient drainage, for which reason large areas are so heavily
charged with salts as to be inimical to most plants. Halophytes
form an important element in the flora of this region. In the most
intense salt areas no plants are to be found at any season. Along
the oueds such shrubs as species of _Tamarix_ and _Zizyphus_ occur,
and juniper may be seen in the more elevated places, such as near
Guelt-es-Stel or further toward Djelfa.
The route followed across the High Plateau ran from Boghari to Ain
Ossera, Guelt-es-Stel, and Djelfa, which is in the midst of the
Saharan Atlas, and from thence to Laghouat.
=BOGHARI TO LAGHOUAT.=
Boghari, situated at the place where the Oued Chelif, having come
across the High Plateau, enters the Tellian Atlas on its way through
them to the Mediterranean, lies on the northern edge of the High
Plateau and in what appears to be a fairly arid region. The oued
at this place is rather narrow and has low banks. In its bed,
in October, were a few pools of water. On either side is the
flood-plain of the oued, several meters in width, sometimes partly
under cultivation. Tilled fields are to be seen to the west and
not far from the town. From the low mountains immediately to the
west of the town the steppes stretch unbroken (save by low hills)
to mountains bounding the southern horizon, possibly 100 miles
straight away. The mountains are the Dj. Sahari, the Saharan Atlas,
beyond which lies the desert.
The vegetation in the neighborhood of Boghari is at present meager
in amount and of small size. Along the banks of the Chelif are
a few tamarisks, and on the plain not far from the oued are a
few specimens of _Zizyphus vulgaris_ and _Pistacia lentiscus_
and other low-growing shrubs. Owing to the large number of sheep,
goats, and camels which are driven through the pass of the Chelif,
or which are kept in the neighborhood by their Boghari owners, few
plants thereabouts fail to exhibit indications of being eaten. In
fact, at Boghari the effects of grazing were first noticed, though
afterwards repeatedly seen. Only such plants as are poisonous,
distasteful, or heavily armed survive the predatory attacks of the
countless numbers of domestic animals.
The habitat of _Pinus halepensis_, which thus extends to the very
edge of the steppes, is to the east and west of the town. To the
west it forms an open forest and is associated with _Quercus
ballota_, growing on the crest and on the northern slopes of
the low mountains. Its abundant fruit, together with acorns, is
gathered assiduously by the Arabs for food. _Juniperus oxycedrus_
and _J. phœnicea_ also occur.
After leaving Boghari and the plain by the Oued Chelif, the route
goes among low, rounded hills for a distance of about 24 kilometers,
when it strikes boldly across the wide-extending plain. The general
appearance of the vegetation, away from the intensely salty chotts,
is that of low-growing shrubs on the plain, and of somewhat higher
shrubs or low trees along oueds. Of the former, perhaps the most
abundant are _Noæa spinosissima_ and _Haloxylon_ sp., and by the
oueds _Tamarix_ sp. and _Zizyphus_ sp. Near Ain Oussera is a wide
belt of _Stipa tenacissima_, the alfa grass, which occurs nearly to
the exclusion of other species, and a second belt of alfa, several
kilometers in width where crossed, was seen very soon after leaving
Guelt-es-Stel. At each of these places were seen large piles of
the grass baled ready for hauling to Algiers.
The alfa, or bunch-grass, covers large areas in Algeria as also in
Spain. In November the long leaves of the grass are dry, tightly
rolled, and rush-formed, in place of being flat as during the
rainy season or period of growth. The species reproduces largely
by means of much-branched rhizomes, from which spring the young,
fleshy leaves, enlarged at the base. In Algeria, “situées en
territoire civil,” there are 543,620 acres of alfa, mostly on
the High Plateau, but a part along the littoral in the province of
Oran, west of Algiers. The leading environmental influence upon the
peculiar distribution of the species is apparently that of rainfall,
reacting in this respect very like plants with storage organs,
avoiding alike regions where the rainfall is excessively heavy or
where it is so little as to cause marked desertic conditions. It
is apparently confined to sandy soils and is replaced by others
wherever the soil of a region (otherwise appropriate for its growth)
is of clay or is charged with any considerable amounts of salts. It
is an important article of export from Algeria. Its total tonnage
is said to amount to 80,000 each year, bringing approximately
$1,500,000. It is sent to England, Belgium, and France, and used
in the manufacture of fine grades of paper, light, strong, and of
a silky texture; also in making baskets, hats, and mats, for which
a superior grade of the grass, commanding especially high prices,
is employed (Kearney and Means, _loc. cit._).
Among other species commonly seen in crossing the steppes are
various salt-bushes, such as _Haloxylon articulatum_ and _Anabasis
articulata_ and especially _Artemisia herba-alba_, with _Tamarix_
and a few specimens of _Pistacia_ along the oueds or where
water conditions are most favorable. Between the belt of alfa
last mentioned and El Masserane, a bordj, there is a broad plain
surrounded by low mountains, which are really the northern extension
of the broad Saharan Atlas, where salt-bushes occur in a formation
several kilometers, possibly 24, across. Here in the summer the
nomads, coming up out of the desert, find grazing for their flocks,
and even in October we saw countless numbers of sheep and goats,
and hundreds of camels, browsing the shrubs.
At El Masserane are specimens of large _Tamarix_, really the size
of small trees, growing near the bordj; and to the south of the
bordj we passed the first dunes encountered on the plateau. These
are part of a series of dunes which were seen to extend to the
horizon to the northeast, as we approached El Masserane, and
which, we were informed, reached as far as Bou Saada, nearly 90
kilometers distant. The dune flora was quite different from that of
the surrounding plain, owing to the total absence of salt plants,
and to the presence, among other species, of a _Tamarix_ and a large
grass, the “drinn” (_Aristida pungens_), which was subsequently
frequently seen.
Soon after passing the dunes the way lay through a country with low
mountains, almost bare of vegetation, where scattering oaks and
junipers constitute the only species of plants, until we reached
the walled town of Djelfa.
=DJELFA TO LAGHOUAT.=
The bleakness and the bareness of the environs of Djelfa come with
a surprise when one considers that the rainfall of the place is not
inconsiderable, about 375 mm., and that the altitude is about 1,110
meters, which insures a fairly low temperature and hence a relatively
low evaporation rate. The sparseness of the vegetation is probably
partly due to the fact that the rainfall does not occur at one or at
two seasons, as nearer the coast, but is distributed fairly evenly
between the four seasons, and also to the long occupancy by the
Arabs and the French, by which possibly most of the useful native
plants, large and small, have long since been destroyed. Somewhat
removed from the town, particularly on the mountains to the west,
is a forest of pines. Along the streets are many shade trees,
as Lombardy poplar, ash, locust, and others, and within the town
limits is a small but fine public park and experimental garden with
a large variety of shrubs and trees.
From Djelfa to Laghouat the road runs through barren mountain passes,
and is dreary and of little interest. Tristram’s description of
the approach to Laghouat, written about 1860, gives very well the
present condition of things:
The next day’s journey was through a rocky desert country. . . . We
afterwards passed a low-lying strip of sand-hills on the west, with
the marks of an ancient ocean beach; on the east a high range of
mountains, with the stratification regular and horizontal. . . . Our
next day’s ride was by a base of a continuous chain of steep
ridges, again with an even water-line very near the crest, and
presenting a singular serrated appearance (the Djebel Lazareg). I
counted no less than 127 little peaks rising above this straight
horizontal line, almost all of them of equal height, like the
crests of a long sea-reef; and lower down the sides were many tidal
strings, if I may so term them. Turning around to our left and
crossing the dry channel of an evaporated and aged “Wed,” we
had some low headlands close behind us—Ras Ainyah of the Arabs,
“Prise d’eau” of the French—the scene of a bloody combat
under General Yusuf. Through an opening between the mountains we
debouched on a wide plain, and suddenly before us stood an isolated
rock. Two cliffs facing each other bore each a bastioned tower,
and in a depression between these lay a town.
The town, whose situation is thus so graphically presented, is
Laghouat, of which the leading present interest lies in the fact that
it is on the very edge of the Sahara proper. From the rocky hills
by the town one can see the serrated Saharan Atlas to the north,
extending northeast and southwest, and, turning, to the south,
an expansive and gently undulating bare plain, stretching without
a break to the horizon.
=LAGHOUAT.=
The ancient Arab town of Laghouat, which is also an important
military post, is a very favorable place from which to begin a study
of the plants and the environment of the plants of the northern
Sahara. Its altitude (780 meters) is greater than that of Ghardaia
(520 meters), as also that of the latter place is greater than the
altitude of Ouargla (150 meters). The annual rainfall of Laghouat
is more than that at either of the places mentioned and more
dependable. The surface of the desert at Laghouat is, for example,
not of one type only, but characteristic of much of the Sahara; that
is, it is mainly stony, a hamada, but there are also sand areas, a
oued and its flood-plain. Finally, the plants growing in the vicinity
of Laghouat are largely typical of those found farther to the south,
as at Ghardaia and Ouargla, or even deeper in the desert. It is of
great interest to observe the change in the habits of the plants,
in their number, distribution, and other features, when one leaves
a less arid region and goes toward a region of gradually increasing
aridity, as when passing southward from Laghouat.
The leading plant habitats are the oasis, the arid plain, and
the dunes. It is not likely that any of these habitats have been
greatly changed because of the settlement by Arabs. The arid plain
and the dunes surely have _per se_ not suffered marked alteration,
and the oasis itself is probably not so different from what it was
formerly, as the great difference in plants growing in it might at
first lead one to suspect. More water is brought to the surface at
present than in primitive times, but if it were possible to remove
all introduced plants, and restore all native plants peculiar to the
oasis, there is no apparent reason why they should not live there
quite as successfully as in earlier times. It does not follow that
there has been no modification of the flora itself, a result of the
founding of a town at the oasis, and it will be pointed out later
that such has surely been the case, but to what extent or in what
way does not appear.