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Full text of "Botanical features of the Algerian Sahara"

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X 



CANNON 



PLATE 1 






s^' 






^x^ 




F.g. 



rket at Laghouat. Jumper, oak, pine, and other kinds of wood, 
each bunch a f-Tr,T^) Io,tH .-xposed for sale. 




Fig. 3. Wood market at Laghouat. Roots of Zizyphus, branches of juniper and 
pine, and pine bark. The latter is said to be used for staining. 



BOTANICAL FEATURES 



OF THE 



ALGEKIAN SAHARA 



BY 



WILLIAM AUSTIN CANNON 







^■^Y"^ 



V 



WASHINGTON, D. C. 

Published by the Carneqie Institution of Washington 

1913 



CARNEGIE INSTITUTION OF WASHINGTON 

Publication No. 178 



Copio& of this Book 
were first issued 

AUG 6 1913 



(}y^ 



\ 



Cl6 



PRESS OF J. B. LIPPIKCOTT COMPANY 
PHILADELPHIA 



CONTENTS. 



PAGE 

Introduction i 

Geographical Characteristics of Algeria 2 

Climate of Algeria 6 

Some Characteristics of the Vegetation of the Tell 15 

The Forests of Algeria 18 

The High Plateau 20 

Boghari to Laghouat 20 

Djelfa to Laghouat 22 

Laghouat 23 

The Oasis of Laghouat 24 

The Plain 25 

The Dunes near Laghouat 27 

The Mountains about Laghouat 28 

Effects of Grazing on Vegetation near Laghouat 29 

From Laghouat to Ghardaia 31 

Region of the Dayas 31 

Daya of Tilrempt 32 

The Chebka 34 

Ghardaia 36 

The Oasis of Ghardaia 38 

The Plain (Hamada) of Ghardaia 39 

The Mountains about Ghardaia 41 

The Valley of the M'Zab 41 

Protected Areas near Ghardaia 42 

Root-Habits in the Ghardaia Region 44 

Leaf-Habits in the Ghardaia Region 49 

Growth and Flowering Habits in the Ghardaia Region 49 

Ghardaia to Touggourt 50 

Ghardaia to Ouargla — Vegetation 53 

Ouargla to Touggourt — Vegetation 56 

Touggourt to Biskra — Physical Features and Vegetation 58 

The Biskra Region 59 

Topography 59 

Plant Habitats of the Biskra Region 60 

Vegetation of the Biskra Region 61 

General Summary and Conclusions 66 

The Environmental Conditions of Plants in Arid Regions 66 

Environmental Features of the Flora of Algeria 69 

Some Effects of Temperature and Rainfall in Southern Algeria 71 

The Soil Relation in Southern Algeria 73 

Root-Characters and Species Distribution in Southern Algeria 76 

The Biotic Factor 77 

Comparison of Some General Features of the Vegetation of Southern Algeria 

and of Southern Arizona 79 



LIST OF ILLUSTRATIONS. 



Plate A. Outline map of Algeria, showing main features of surface 
drainage. 
PI. I , fig. I . View of the oasis of Laghouat. 

2. Wood market at Laghouat. Juniper, oak, pine, and other kinds of wood, 

each bunch a camel load, exposed for sale. 

3. Wood market at Laghouat. Roots of Zizyphus, branches of juniper and 

pine, and pine bark. The latter is said to be used for staining. 
PI. 2, fig. 4. Shoot-habit of Acanthyllis tragacanthoides. Laghouat. 

5. Shoot-habit of Zollikoferia spinosa. Laghouat. 

6. Acanthyllis tragacanthoides on sandy plain. Laghouat. 

7. Zollikoferia spinosa in habitat, plain (hamada). Laghouat. 

PI. 3, fig.^ 8. Detail of north slope of Nomad Mountains, where Zollikoferia spinosa 
is the dominant species. Laghouat. 
9. Vegetation of plain (hamada) at Tilrempt. The conspicuous shrub is 

Haloxylon articulatum. 
10. The daya of Tilrempt from the plain, showing the character of the 
depression. 
PI. 4, fig. II. Near view of the daya of Tilrempt. The fortified stage station, bordj, 
and a nomad camp are to be seen. The flattened, level, lower surface 
of the trees is the eflfect of grazing, mainly by camels. 
12. Jujube {Zizyphus) shrubs and betoum (Pistacia) at the daya of Tilrempt. 
PL 5, fig. 13. A young specimen of betoum in the midst of a protecting jujube at the 
daya of Tilrempt. 

14. Leaf and shoot habit of the jujube (Zizyphus lotus). Daya of Tilrempt. 

15. Leaves of the betoum [Pistacia atlantica) from the daya of Tilrempt. 
PI. 6, fig. 16. South wall of the valley of the Oued M'Zab at Ghardaia, 

17. Detail of an eroded bank of the Oued M'Zab at Ghardaia. The over- 
hanging stratum is hardpan similar to the "caliche" of southwestern 
United States. 
PI. 7, fig. 18. Shoot-habit of Haloxylon articulatum, from the plain near the daya of 
Tilrempt. 
19. Agriculture at Ghardaia. The fields are divided into plots about 3 by 4 
feet in size, for the more economical use of water. Young barley is 
shown growing (November). 
PI. 8, fig. 20. Vegetation in upper part of a "draw" on plain north of the M'Zab 
Valley, Ghardaia. 
21. Situation of square No. 2, on plain north of valley at Ghardaia. 
PI. 9, fig. 22. Capparis spinosa at base of valley wall at Ghardaia. 

23. Leaves of Capparis spinosa from Ghardaia. 
PI. 10, fig. 24. Leaf-habit of Dcemia cordata. Ghardaia. 

25. Shoot-habit of Salvia agyptica. Ghardaia. 

26. Upper surface of rocks, showing small incrusting lichens, on a low moun- 

tain about 5 km. north of M'Zab Valley, Ghardaia. 
PI. II, fig. 27. Habitat of Peganum harmala, at Melika, Ghardaia. 

28. Shoot and leaf habit of Peganum harmala, from Ghardaia. 
PI. 12, fig. 29. Habit of Henophyton deserti at Ghardaia when growing in a protected 
situation (cemetery). 
30. Leaf -habit of Henophyton deserti. Ghardaia. 
PI. 13, fig. 31. View in a cemetery at Ghardaia, to show the relatively abundant vege- 
tation. 
32. View in an M'Zabite cemetery, Ghardaia. Haloxylon articulatum is the 
leading species shown. 
PI. 14, fig. 33. Habit of Deverra scoparia, from plain about 3 km. north of M'Zab Valley, 
Ghardaia. 
34. Root-habit of Gymnocarpos fruticosum, from plain about 3 km. north of 
M'Zab Valley at Ghardaia. 
PI. 15, fig. 35. Root-habit of a mature specimen of Peganum harmala, from the floor of 
the M'Zab Valley near Ghardaia. The soil at the place is compara- 
tively deep. 



LIST OF ILLUSTRATIONS. V 

PI. 15, fig. 36. Root-systems of Helianthemum sessiliflorum (right), Haloxylon articu- 

latum, and Nolletia chrysocomoides (left), from the flood-plain of the 

Oued M'Zab, Ghardaia. 
PI. 16, fig. 37. Shoot and root habit of Citrullus colocynthis. Oued M'Zab, Ghardaia. 

38. Euphorbia guyoniana, in the valley of the Oued M'Zab at Ghardaia. 
PI. 17, fig. 39. Habit of Euphorbia guyoniana. Ghardaia. 

40. To the left, shoot of Centaurea sp., showing effect of grazing; to the right, 

shoots of Teucrium pseudo-chamcBpitys. From Ghardaia. 
PI. 18, fig. 41. Habit of Salsolasp. (below) and Echinopsilon muricatus, from the M'Zab 

Valley, Ghardaia. 
42, Ghardaia to Ouargla. View overlooking the hamada about 28 km. from 

Ghardaia. The relatively abundant vegetation is associated with a 

light cover of sand over the area shown. The leading species are 

Aristida, Deverra, and Haloxylon. 
PI. 19, fig. 43. Retama retam, in dunes about 58 km. from Ghardaia. 

44. Dates at the Bordj Zolfana, about 58 km. from Ghardaia — one of two 

wells encountered between Ghardaia and Ouargla. 

45. Ghardaia to Ouargla. View overlooking flood-plain of the Oued M'Zab, 

or a tributary of this oued. The adjacent upland is apparently with- 
out plant life. 
PI. 20, fig. 46. Vegetation on edge of the Oued M'Zab, about 63 km. east of Ghardaia, 
showing habitat of Rhantherium adpressum in foreground. 

47. Sandy flood-plain of the Oued M'Zab, about 63 km. from Ghardaia. 

Retama, Genista, and Ephedra are the leading plants in this place. 

48. Habit of Ephedra alata in habitat shown in figure 47. This specimen was 

1.5 m. high. 

PI. 21, fig. 49. View of habitat of Ephedra alenda, 138 km. from Ghardaia. 

50. Detail of suckering habit of Ephedra alenda, from habitat shown in 
figure 49. 

PI. 22, fig. 51. Vegetation, mainly Ephedra and Retama, of the western edge of the 
Chott Mellala. 
52. Approach to western edge of the Chott Mellala, showing characteristic 
rounded hills, or mamelons. 

PI. 23, fig. 53. View between the Ouargla plain and the Chott Mellala, showing char- 
acteristic appearance of eroded hills. 

54. Looking toward the Ouargla plain (reg). 

55. Shallow well about 25 km. north of Ouargla. 

PI. 24, fig. 56. Ouargla to Touggourt. Leaf-habit of Limoniastrum guyonianum. The 
surface of the leaves is covered with an incrustation of salts. 
57. Habit of Limoniastrum guyonianum. About 25 km. north of Ouargla. 
PI. 25, fig. 58. Vegetation of the reg desert, about 25 km. north of Ouargla. Ephedra 
and Retama are the leading species of the area — a spreading dune. 
59. Shoot-habit of Halocnemon strobilaceum. About 28 km. north of Ouargla. 
PI. 26, fig. 60. Habit of Halocnemon strobilaceum on the edge of a chott, about 28 km. 
north of Ouargla. 
61. Shoot and leaf habit of Anabasis articulata, about 32 km. north of 
Ouargla. 
PI. 27, fig. 62. Detail of the shoot-habit of Salsola tetragona?, about 25 km. north of 
Ouargla. 
63. Habit of Nolletia chrysocomoides near the edge of a chott, about 80 km. 
north of Ouargla. 
PI. 28, fig. 64. Tamarix sp. as a sand-binder near Bled-el-Amar, south of Touggourt. 

65. Biskra. Habitat of Euphorbia guyoniana, looking toward the Djebel 
Maouya, with the Chaine de Sfa in the background. 
PI. 29, fig. 66. Characteristic vegetation on the north slope of the Djebel Bou Rhezal, 
Biskra. Haloxylon scoparium is a prominent species. 
67. North base of Ed Delouatt hills, west of Biskra, showing the low facing 
dunes. To the right is a glimpse of an oued which pierces the hills in the 
middle distance. 
PI. 30, fig. 68. Flood-plain of the Oued Hamman es Salahin, Biskra. Halophytes of 
various species occupy the foreground. 
69. Habitat of Phelypcea violacea shown in figure 70. 
PI. 31, fig. 70. Young shoots of Phelypaa violacea, at north base of Ed Delouatt hills, 
Biskra. 
71. Habit of young specimens of Phelypcea. Except for about 15 cm., plants 
were buried by sand. Biskra. 



VI LIST OF ILLUSTRATIONS. 

PI. 31, fig. 72. Asphodelus sp. at north base of Ed Delouatt hills, Biskra. Photographed 

in March. 
PL 32, fig. 73. Detail of square No. i, on low hills north of Biskra. 

74. Vegetation of north slope of the low hills which are north of Biskra. 
Ferula vasceritensis is the perennial appearing in the figure. 
PI- 33i fig- 75' Detail of square No. 2, near area shown in fig. 74. Ferula and Haloxylon 
are leading species. 

76. Root-habit of Haloxylon scoparium, from a wash near Biskra. 

77. Young shoots and mature roots of Ferula vesceritensis. North of Biskra. 
PI. 34, fig. 78. Root-habit of Fagonia growing on edge of a wash. Biskra. 

79. Large lateral root of Haloxylon, with numerous deciduous rootlets, no 

longer functional. 

80. Shoot-habit, taken from above, of Fagonia from the flood-plain of a 

small oued near Biskra. 

PI- 35i fig- 81. Spring annuals, March 17, on north slope of the Djebel Bou Rhezal, 
Biskra. 
82. Root and shoot habit of Peganum harmala, Biskra. The main root is 
especially well developed, although the species has a generalized 
root-system. 

PI. 36, fig. 83. Annuals growing with Peganum, near Biskra. 

84. General view of the north face of the Djebel Bou Rhezal, Biskra. Appar- 
ently barren, plants are rather numerous in the rock crevices and 
small washes of the mountains. 



BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 



INTRODUCTION. 

The present paper is designed to give the resiilts of some field-work in 
southern Algeria in the autumn of 1910 and the spring of 191 1. The chief 
purpose of the tour was to examine the more obvious features of the physio- 
logical conditions prevalent in the region in question and, in connection 
with these observations, to make some detailed studies of the root-habits 
of the most striking species of the native flora. The route lay through the 
Atlas Mountains, over the High Plateau, and for some distance into the 
Sahara itself, returning by a somewhat similar way farther to the east. 
The country traversed was extremely varied in topography and in plant 
life, and probably the most southern regions seen may be taken as typical 
of much of the western Sahara. The distance covered in the more arid 
portions of the colony was about 1,000 miles. 

An English-speaking toiuist, or any tourist for that matter, is some- 
thing of a curiosity in southern Algeria. We were said to be the second 
party of "Englishmen " who had passed over the Ghardaia-Ouargla country 
in twenty-five years. 

Leaving Algiers in October, diligence was taken to Ghardaia, the most 
important town in southern Algeria and the end of the diligence service. 
Beyond Ghardaia travel is by camel only. The diligence journey, if made 
without stop, requires six days, running night and day, except the first 
day's run, which is by day only. Pauses in the journey to Ghardaia were 
made at the leading towns or stage stations (bordj), thus affording oppor- 
tunity to observe several localities in the High Plateau as well as the por- 
tion of the desert just south of the Saharan Atlas. Stop-overs were made 
thus at Medea, Boghari, Djelfa, Laghouat, and Tilrempt. A fortnight was 
passed at Ghardaia, where the environs of the city were quite thoroughly 
explored. As there are no roads between Ghardaia and Ouargla, or between 
Ouargla and Touggourt, it was necessary to organize a small camel-train, 
engage a cameleer (sokhrar) and servants, and make special arrangements 
for the trip. Nine days were required for the portion of the journey to 
Touggourt via Ouargla. At Touggourt diligence was again taken for 
Biskra, two days' journey. The return journey to Algiers from Bislo-a was 
broken at Batna for the purpose of visiting the fine forest of cedar (Cedrus 
atlantica) in the mountains not far from the town. When Bislcra was re- 
visited, in the spring of 191 1, the northern portion of Algeria was crossed 
on the way from Tunis, this affording an opportunity to observe some- 
thing of the picturesqueness of the mountainous regions as well as the 
spring flora. 

1 



2 BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 

I wish to take this early opportunity to acknowledge my appreciation 
of assistance received from different persons diiring the course of the Alge- 
rian study, or as a means of preparing for it. I am especially indebted to 
Prof. H. J. Hall, of Leland Stanford University, who was my companion 
in Algeria and whose knowledge of the American deserts made his advice 
doubly valuable. Dr. Keltic, secretary of the Royal Geographical Society, 
provided letters and infonnation of much use. Dr. Trabut, government 
botanist of Algeria, whose acquaintance with the cotmtry is extensive, very 
kindly identified all plants sent him and gave valuable aid in other ways. 
The map (plate A) was prepared expressly for this study by Mr. Godfrey 
Sykes. 

In a country where travel away from the beaten path is not without 
discomfort, it is important that the way be made as smooth as possible, 
not alone for comfort but for personal safety as well, and it is therefore a 
pleasure to acknowledge the many kindnesses shown by the civil and mili- 
tary authorities of the French colony, as also by the American consiil and 
vice-consul at Algiers. 

GEOGRAPHICAL CHARACTERISTICS OF ALGERIA. 

The French colony of Algeria is of large extent and possesses a highly 
varied topography and great range in climate. With an all-land connec- 
tion with the continent of Europe in earlier geologic times, the flora and 
fauna of this portion of northern Africa are closely allied to the fauna and 
flora of southern Spain, France, and Italy. 

Algeria lies to the south of the Mediterranean Sea, between Tunis to the 
east and Morocco to the west. The northern portion extends somewhat 
beyond latitude 37°, or that of southern Spain, southern Greece, and the 
southern part of Asia Minor. The limit of the colony on the south is 
indefinite, reaching to about latitude 21°. Thus east and west the extent 
is about 650 miles, and north and south 1,200 miles. 

The most important topographical features of the northern part of 
Algeria are the several mountain masses which together constitute the 
Atlas range. Lowest in Tunis, where the Atlas Mountains do not exceed 
5,000 feet altitude, they attain their greatest height in Morocco, over 13,000 
feet. In Algeria an altitude of about 7,500 feet is reached in the Aur^s, Dj. 
Chelia, and in the Great KabyHes. In the eastern portion of Algeria the 
mountains extend to the coast, but farther west a narrow strip of lowland 
separates them from the sea. In the east (in the department of Constan- 
tino) they constitute a single general upHft, although made up of several 
groups, but as one proceeds westward the mountains separate into two 
ranges, which at the Morocco border are about 125 miles apart. The two 
ranges have been called by various names, among which are the Great 
Atlas for the southern range and the Little or Maritime Atlas for the north- 
em one. But it seems best to use the names Atlas of the Sahara or Saharan 



GEOGRAPHICAL CHARACTERISTICS OF ALGERIA. 3 

Atlas and Atlas of the Tell or the Tellian Atlas, names which are self- 
explanatory. The Tellian Atlas and all territory between this range and 
the Mediterranean Sea is known as the Tell, or the land of hills. This is 
the most important part of Algeria from an agricultural standpoint, and 
furnishes grain and other products. Here also are the most important 
forests, oak, pine, and cedar. Between the two ranges of the Atlas lies 
the region of the steppes or plateaus, in this study referred to as the 
High Plateau, inasmuch as the average altitude is over 3,000 feet. The 
steppe region is highest in the west and is wedge-shaped, in conformity 
to the bounding mountains. In the eastern portion it breaks up into 
mountain valleys. The topography of the High Plateau is monotonous. 
The surface is gently rolling, and here and there are undrained depres- 
sions, or chotts, where salts accumulate. In rainy seasons the chotts 
contain water, but in the arid summers they are dry. The region of the 
steppes is of no agricultural value, although, as will appear below, the 
harvesting of the alfa grass, which occupies vast areas, is of considerable 
importance. 

South of the Saharan Atlas lies the desert, comprising about 2,000,000 
square miles, the topography of which is extremely varied. For present 
purposes it is sufficient to say that in the extreme southern portion of 
the Algerian Sahara, and crossed by the Tropic, there is an extensive 
highland, the plateau of Idghagh, where an elevation exceeding 5,000 feet 
is reached. All of the Sahara to the west of this plateau, or to the west 
of a line drawn north from it, appears to be above sea-level (much of it 
having an altitude of 1,000 feet), and of greater geological age than that 
portion of the desert lying to the east. North from the plateau of Idghagh 
the country gradually descends to the depression of which the great Chott 
Melghir is a part, a region below the level of the sea. Here extends also 
one of the longest oueds of the Sahara, the Oued Igharghar, which takes 
its rise in the plateau of Idghagh and empties in the Chott Melghir, an 
entire length exceeding 700 miles. In the western part of the Sahara the 
surface descends to the Atlantic, but in the eastern part it falls away to 
the Mediterranean. 

Turning now to consider the part of southern Algeria with which this 
study especially deals — lying between Laghouat and Ghardaia, between 
Ghardaia and Ouargla, and between the latter place and Biskra, all to the 
south of the Saharan Atlas — we find topographical details which are prob- 
ably representative of much of the rest of the Great Desert. Laghouat 
has an elevation of 2,400 feet. It lies on the northern edge of the region 
of the dayas. This region is characterized by the poor development of 
its drainage and has a slightly undulating surface vrith frequent depres- 
sions, each the center of an area of rather small extent, from which it 
receives flood-waters. The dayas differ from the other undrained areas, 
the chotts, in that they do not contain an excess of salt, owing probably 



4 BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 

to efficient subdrainage. In the region of the dayas the surface falls away 
to the south or the southeast until the region of the Chebka is reached, 
which extends to the territory of the Beni M'Zab. In the Chebka low and 
flat-topped mountains are so irregularly disposed as to give rise to the 
name, meaning a net; they are separated by valleys, narrow toward the 
northern portion of the region, but expanding into small plains as one 
proceeds towards Ghardaia. Ghardaia, the country of the Beni M'Zab, 
marks the southern limit of the Chebka. At Ghardaia the altitude is 
1, 600 feet. Between Ghardaia and Ouargla are undulating stony plains, 
the Gantara (hamada), large salt spots, the chotts, and a prominent range 
of sand mountains, areg desert, possibly 1,000 feet high. At the eastern 
edge of the Gantara the general level of the country drops suddenly 
about 200 feet to the Ouargla plain (reg desert), with an altitude less 
than 500 feet; this is an eroded flood-plain of the Oued Igharghar or its 
tributaries. 

There are no navigable rivers in Algeria. The most important river is 
the Chelif, which takes its origin in the Saharan Atlas, crosses the High 
Plateau, breaks through the Atlas of the Tell, and, turning westward, 
traverses obliquely the Tell for a distance of about 108 miles before dis- 
charging into the sea. The Chelif is the only stream which rises in the 
Saharan Atlas and pierces the northern range. To the south of the Saharan 
Atlas are several important oueds. One, the Oued Djedi, rises near Aflou 
and goes easterly, past Laghouat, until it reaches the Chott Melrir, south 
of Biskra; two others, the M'Zab and the Nessa, drain the region of the 
Chebka, and taking an easterly or a southeasterly direction reach the Oued 
Rirh or its upper extension. The Oued Rirh constitutes the northern por- 
tion of the great Oued Igharghar, or a tributary of this oued, and extends 
about 60 miles north from Touggourt to the Chott Merouan. The region 
of the Oued Rirh is of great economic importance from the production of 
dates, made possible through the development of artesian wells by the 
French government. The oueds as a whole are very like the arroyos of 
the southwestern portion of the United States, in that they carry water 
for a small portion of the year only, v/hen the torrential rains fill them 
with a muddy, rushing flood. 

In the plains adjacent to the oueds, at Ghardaia especially, the natives 
usually dig their wells, from which water for domestic as well as for irri- 
gating purposes is obtained. The flood-water of the oueds is also diverted 
into ditches, or impounded for later use, although the latter has not met 
with uniform success. The depths at which water has been foimd vary 
greatly. At Ouargla the water lies within 3 feet of the surface, although 
there are also very deep artesian wells, and at Ghardaia it varies from 10 
to 50 feet or more. At the daya of Tilrempt the water in the deepest wells 
stands as deep as 300 feet; it is drawn in a very primitive fashion for pur- 
poses of watering flocks and for the bordj. The heaviest vegetation is to 



GEOGRAPHICAL CHARACTERISTICS OF ALGERIA. 5 

be found along the oueds and the nearby flood-plains. Here the water 
relations are the most favorable and the oueds constitute highways along 
which plants venture into the desert from the more humid regions. 

Very little study appears to have been given the soils of Algeria. It has 
been stated that there are vast areas of light, sandy soils, and also exten- 
sive tracts of marls, clays, and alluvial soils.* Gypsum is an important 
element in the soils, both those of the oases and probably of the open 
desert also; it occurs in great quantity in the large chotts of the desert, 
along with common salt and other salts. In the soils of the oases it acts 
as a cementing material, "uniting the finer soil-grains into aggregates 
which give the soil a much more sandy appearance than would be suspected 
from the results of mechanical analysis." At Laghouat and at Ghardaia 
a light-colored, hard substance, closely resembling the "caliche" of the 
southwestern United States, was seen incrusting stones, filling cracks in 
rocks and crevices between rocks, and in places forming a stratum, hori- 
zontally placed (15 cm. more or less in thickness) underneath the superficial 
soils. This is extremely hard and can be broken or cut with difficulty. 
In the valley of the M'Zab, where it constitutes a heavy substratum, it 
appears to be impervious to water. This hardpan is used as threshing 
floors by removing the superficial soils. 

An unexpectedly small amount of sand was observed over the route 
traversed. Near the southern edge of the High Plateau a sand belt was 
encountered and a long stretch of low dunes was seen leading to the east- 
ward, w^hich were said to reach nearly to Bou Saada; and again at Laghouat 
there are dunes to the east of town as well as to the west. Low dunes 
were seen in the valley of the Oued M'Zab, and sand mountains, possibly 
250 meters high, were passed on the way from Ghardaia to Ouargla. Be- 
tween Ouargla and Touggourt, also, sand was encountered and the w^ay 
lay across about 12 miles of low dunes; to the north of Touggourt dunes 
are also to be seen; and finally, some sand is to be found in the neighbor- 
hood of Biskra. Although, thus, relatively little sand was met, much of 
the entire portion of southern Algeria is covered by sand. Large areas of 
sand-covered country lie to the east of the Oued Rirh, and especially south- 
east of Touggourt, and also to the west of Ghardaia there is said to be a 
large dune-covered territory. For the most part, however, the surface of 
the plains crossed is covered with large or small stones, mingled \%'ith which, 
or beneath which, there is a rather fine clay-like soil. This constitutes the 
hamada, or stony desert, of which the largest portion of the surface of the 
Sahara is probably composed. Where stones are largely absent and the 
soil is fine, usually of flu\'ian origin, the formation is known as "reg." Reg 
desert was encountered at and north of Ouargla, in the drainage of the 
Igharghar or its tributaries, and south of Biskra. The latter may not, 

*Kearney and Means, Agricultural explorations in Algeria, Bui. No. 80, Bur. Plant 
Ind., U. S. Dept. Agric, 1905. 



6 BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 

strictly speaking, be reg, but a wide-stretching bajada, and the soil is 
probably only in small part deposited by rivers. 

CLIMATE OF ALGERIA. 

The climate of Algeria is mild and temperate. This is due to several 
factors, among which are its situation relative to the Mediterranean on 
the north and to the Atlantic on the west, as well as to the great desert 
which constitutes its southern portion, the great variation in topography, 
and the fairly low latitude. Taking the colony as a whole, there is a great 
range in temperatiu-e, precipitation, relative huinidity, and evaporation, 
to mention only such climatic features as have been reduced and are re- 
corded; and the range in the intensity and in the quality of the light must 
also be great. The climate of the northern portion of Algeria is coastal, 
while that of the southern portion is continental. 

The distribution in time and in space and the amount of precipitation 
are of the greatest importance as climatic features of Algeria. The rain- 
fall is heaviest on the littoral, and especially heavy in the eastern portion 
of the littoral. An average of i,ooo mm. is reported from the immediate 
vicinity of the sea,* and as one goes southward the amount of precipita- 
tion rapidly becomes less. In the Tell the average rainfall is 570 mm., 
while on the High Plateau it is 310 mm. On the desert the rainfall is un- 
certain both in amount and in time, except that when rains occur the time 
coincides with the rainy season of northern Algeria. At Biskra the annual 
precipitation is 199 mm., at Laghouat it is 198 mm., at Ghardaia it is 114 
mm., and at El Golea it is 47 mm. In many places in the western Sahara, 
five years or more go by without fall of rain. 

The differences in the geographical distribution of precipitation vary 
from year to year, as may be illustrated by referring to that for the year 
1908, which may be compared with the normal usual distribution as given 
above. In the northern portion of the country more rain than usual was 
reported; for example, there was over 1,000 mm. on the littoral east of 
Algiers, and over 500 mm. on the High Plateau, but on the desert the 
amount was somewhat less. At Laghouat it was 161 mm., at Ghardaia it 
was 89.2 mm., and at Ouargla it was 28 mm. 

Besides the differences in amount of yearly rainfall, well-marked seasonal 
amounts of precipitation are also to be noted. In the northern portion of 
the colony rains are likely to occur in \vinter and spring, the summer and 
early autumn being dry ; and as one goes south of the Saharan Atlas nearly 
the same conditions obtain; that is, the rains usually fall during the rainy 
season of the coast. The seasonal distribution of rain for the Tell, includ- 
ing the stations of the Httoral, the High Plateau, the Saharan Atlas, and 
the desert, for a series of years including 1908, is given in table i. 

* A. Engler, Die Vegetation der Erde IX. Die Pflanzenwelt Afrikas. i Bd., 1910, 
page 902. 



CLIMATE OF ALGERIA. 







Table 


I. — Seasonal distribution of rain. 


Season. 


Tell (10). 


High 
Plateau (8). 


Saharan 
Atlas (10). 


Desert (6). 


Remarks. 


Winter. . 
Spring. . 
Summer 
Autumn 


mm, 
469.9 
300.0 
38.1 
287.3 


mm. 

1 19.3 (SO.8) 
80.S (95-0) 
66.S (3S.8) 

139.S (S8.S) 


mm. 

113.5 
88.2 
50.4 

123. 1 


mm. 
37.4 
39.0 
3.7 
19.6 


The Tell is represented by Fort Na- 
tional; the High Plateau by Geryville 
(with Ain Sefra, for 6 years, in paren- 
theses); the Saharan Atlas by Djelfa: 
the desert by Ouargla. The number of 
yearly records on which averages are 
computed are given at the bead of each 
column in parentheses. 



The seasonal percentages of precipitation give a more graphic concep- 
tion of the rainfall conditions for the four physiographic provinces. In 
the Tell this percentage in winter is 42, in spring 27, in summer 4, and in 
autumn 27. On the High Plateau the percentages are 30, 20, 16, and 34 
for the four seasons respectively. In the Saharan Atlas 30 per cent of the 
rain occiurs in winter, 24 in spring, 13 in summer, and 33 in autumn. In the 
desert the percentages of rainfall are 37, 39, 4, and 20* for the four seasons. 

It is of interest also to note the number of days on which the rain fell 
on an average each year over a period running from 7 to 12 years. Thus 
at two typical stations on the Tell rain was reported on 102 and 118 days; 
at two stations on the High Plateau it rained 65 and 83.8 days; at a station 
in the Saharan Atlas rain was reported on 70 days; at desert stations, at 
Ouargla rain fell on an average 14.2, and at Laghouat 49 days each year. 
As a comparison, it may be mentioned that for ten years at Wady Halfi, 
Egyptian Sudan, there were only 22 days on which rain-drops were seen 
to fall. (Engler, loc. cit.) 

The amount of precipitation varies greatly for the different desert sta- 
tions, usually becoming less as one goes south from the High Plateau. As 
has already been mentioned, the average rainfall at Laghouat, which lies 
at the southern base of the Saharan Atlas, is 198 mm., the average at 
Ghardaia is 114 mm., while that at El Golea is 47 mm. The latter station 
is about 225 miles south of Laghouat, in the midst of the Sahara, The 
amount of rainfall, however, is greatly influenced by altitude, although 
lack of adequate precipitation data for the desert makes impossible a 
detailed presentation of this phase of the subject. As the amount of the 
yearly precipitation is less in the extreme southern part of Algeria than it 
is nearer the Saharan Atlas, where the altitude also is greater, it might be 
expected that the number of rainy days would vary in a like manner. Such 
records as are at hand, however, do not show this to be the case. For in- 
stance, at Ouargla rain falls on an average 14.2 days, average of 7 years, 



* The seasonal distribution of rain (by percentages) 
is somewhat different from that given by Engler, 
which is given in the accompanying table. 



Season. 


t^ill^ell. 


High 
plateau. 


Winter. . 
Spring . . 
Summer. 


41 36 

27 32 

4 7 


II 



8 



BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 



while the rainfall is go. 2 mm.; yet at El Golea, with a rainfall of 47 mm., 
there are 23.4 rainy days each year.* 

On the desert the rains are often of a torrential nature, as facts presented 
above would indicate, and sometimes as much rain falls within a few hours, 
or even a few minutes, as usually occurs in an entire year. How much of 
the annual precipitation is of this character and how much is of the non- 
torrential kind the usual summaries leave entirely out of the account. It 
is well known that the former type of storm is more destructive and less 
useful to plants than the latter type. To illustrate the irregularity of the 
rainfall in the northern Sahara the monthly precipitation at Ouargla for 
several years is presented in table 2. 

Table 2. — Rainfall at Ouargla, in millimeters. 



Year 


Amt. 


No. of 
days Jan. 

rain 


Feb. 


Mar. 


Apr. 


May 


June 


July 


Aug. Sept. 


Oct. 


Nov. 


] 
Dec. 


1900 
1901 
1902 
X903 
1904 
190S 
1906 
1907 




70.'s 
135.6 
35-0 

2x0.0 


I 
18 

8 
14 
26 

18 





55.0 
20.0 

1 5.0 











68.2 




II.3 



2.0 
67 








4.0 
325.0 









16.2 









20.0 








4.0 





1.8 





80.0 









41.0 
5.0 




46.4 

9.0 

80.0 
3-3 




II. 

30.6 

4.0 

3.8 





50.0 

2.0 
1.3 



The seasonal distribution of rainfall at four desert stations shows also 
marked irregularities. The distribution (in percentages) is given in table 3 . 
Table 3. — Seasonal distribution, in percentages, of rain. 



Station. 


Winter. 


Spring. 


Summer. 


Autumn. 


Ouargla 

Laghouat 

Ghardaia 

Touggourt 


37 
II 
15 
13 


39 
27 
23 
30 


4 
31 
13 

3 


20 
31 
49 
S3 



The relative humidity at the desert stations is often very low, sometimes 
running in midsummer between 7 and 9 per cent for 6 days, and occasion- 
ally being too low to measure with the instruments employed. The mean 
relative humidity (table 4) shows the general very dry condition of the air 
of the desert as contrasted with a station in the Tell, and also indicates 
something of the monthly variations in this factor experienced among the 
desert stations themselves. The averages given are from 4 to 8 years, 
except the mean annual for In Salah, which is for 2 years only. 
Table 4. — Mean relative humidity, in percentages. 



Station. 


Jan. 


Feb. 


Mar. 


Apr. May 


June 


July 


Aug. 1 Sept. 


Oct. 


Nov. 


Dec. 


Year. 


Ouargla 

El Golea 

In Salah 

Ft. National 


61.0 
60.8 
51.5 
87.4 


S8.6 
S6.8 
48.0 
80.3 


60.3 
41-3 

45-5 
87.6 


51.2 52.0 

41.3 41.0 

40.4 34-6 
86.6 96.6 


49.0 
31.3 
32.0 
80.4 


44.1 
28.S 
23.4 
75-8 


44.7 
31.8 
24.6 
62.8 


50.7 
34-8 
17.2 
80.2 


S6.8 

37.1 
38.0 
87.7 


591 
58. 1 
52.2 
92.8 


52.7 
65.1 
58.7 
88.4 


54.6 
45.5 
42.6 
85.1 





* The most recent records available, 1897-1908, do not give a satisfactory account of 
the precipitation on the desert. For instance, meteorological records covering eight 
years for EI Golea do not report on the rainfall. Records of five years at In Salah take 
the rainfall into account on one year only, and on that year no precipitation occurred. 



CLIMATE OF ALGERIA. 



A consideration of the evaporation statistics of Algeria for the year 1908 
shows some interesting relations. It has already been observed that the 
rainfall along the coast is less in the west than in the east, and it will ap- 
pear below that as a rule the temperature of the western portion is lower 
than that of the corresponding regions lying to the east. In both rainfall 
and temperature, however, the greatest variation is to be found as one 
goes inland, when decreasing rainfall and higher temperatures are encoun- 
tered. A similar relation obtains in evaporation, which becomes continu- 
ously greater as the distance from the coast increases; that is, the average 
evaporation for stations on the High Plateau is greater than for stations 
in the Tell, and the evaporation at desert stations is greater than the evapo- 
ration on the High Plateau. The total average evaporation for the year, 
in millimeters, for 5 stations on the littoral, was 1,365.3; for 7 stations in 
the Tell it was 1,378.6; for 4 stations on the High Plateau 2,352.2, and for 
3 stations in the desert, 3,977.5. The least evaporation reported was 
at Bouzarea, which was 989.9 mm., and the greatest was at Ghardaia, 
5,309.7 mm.* 

Table 5 gives in detail the monthly as well as the total evaporation for 
the year at three desert stations and at Algiers for 1908. 

Table 5. — Evaporation in millimeters, 1908. 



Station. 



Jan. Feb. Mar, 



Apr. i May 



June July '< Aug. i Sept. I Oct. 

ill 



Nov.! Dec. 



Year. 



Laghouat | 88.9 102.3 143.4 203.1 I289.2 373.9 I421. 2 379.6 I264.8 1 173-9 153-8 'iS9.2 27S3 

Ghardaia 172.4 233.4 340-7 '528.7 611. 7 699.1 749-2 693.0 468-8 329-4 257.7 225.5 ' 5309 

Touggourt .... 163-9 240.51274-3 385-2 459-4 565-8 487.3 329-4 222.6 166. 1 142.31 .... 

Algiers j 84.2 96.8 90.5 II18.3 151.8 158.6 [l75-0 205.0 165-5 129.0 136.1 143.2:1654 



For a better personal appreciation of the rate of evaporation, as well as 
for the purpose of comparison, I arranged an apparatus to tell the water- 
loss from a free water-surface. It was also desirable to determine the 
relative evaporation of the day and night. As employed, the apparatus 
consisted of a fiat tin dish, with parallel sides, lo cm. in diameter. To the 
side was attached, by means of a rubber stopper, a bent glass tube of small 
diameter. The water-loss was read on this tube. Observations were made 
at Laghouat and at Ghardaia. Following is a summary of the results obtained 
at Ghardaia: For a period of 7 days, after November 10, the daily water- 
loss between 7 a.m. and 7 p.m. was as follows: 5, S, 8.5, 10.5, 13, 9, and 7.5 
mm. The evaporation between 7 p.m. and 7 a.m. was so slight, i mm. 
more or less, that it could not be well determined by the apparatus used. 

A good idea of the intensely arid character of the Algerian climate, taken 
as a whole, is to be obtained by a study of the relation between the total 

* Unless otherwise stated, the climatological statistics given in this paper were taken 
or compiled from Observations M^t^orologiques du Riseau Africain, 1907-1908. The 
evaporation data are based on readings of the Piche evaporimeter. The amount of 
evaporation given in the text can be reduced to the evaporation from a free-water 
surface bj' multiplying by 0.737 (Meteorological Notes, J. I. Craig- Cairo Scientific 
Journal, vol. vi, May 191 2). 



10 



BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 



rainfall and the total evaporation, based on the official cHmatic reports. 
In tables 6 and 7 the report for the year 1908 is used. The figures repre- 
sent the ratio f-j between evaporation and rainfall, in which the amount of 

evaporation is used as the numerator and the amount of precipitation as 
the denominator. In the monthly evaporation-rainfall table (table 6), in 
all cases where no rainfall was reported for the month it was called i mm. 
In table 7, however, which gives the seasonal evaporation-rainfall ratio, 
the actual figures of the government report were in all cases employed, 
since there was no season during the year 1908, even in southern Algeria, 
when no precipitation occurred.* 

Table 6. — Evaporation-rainfall ratio, monthly, 1908. 



Station. 



Jan. Feb. Mar. Apr. May. June.ijuly. Aug. Sept. Oct. Nov.] Dec. 



May. 


June. 


July. 


131 


5.4 


23.6 


8.8 


10.3 


29.7 


17.4 


8.5 


59.0 


22.3 


ir.7 


219.0 


8.3 


4.8 


53.7 


13.5 


II. 8 


149.0 


3.7 


192 


42.S 


18.8 


18.5 


77.8 


2.2 


6.9 


86.7 


46.S 


33.4 


24.4 


252.0 


2.8 


Q.8 


6.1 


165 


43.5 


5.03 


270 


6.1 


12.4 


63.1 


16.4 


2.5 


l6.7 22.5 


7.0 


373 421.0 


38.9 


699 ii66.o 


369.0 


465 


S09.0 



Nemours 

Cape Falcon . . 

Oran 

Algiers 

Bouzarea 

Maison-Car^e . 
Ft. National . . 
Sidi-bel-Abb^s . 

Saida 

Batna 

Tebessa 

Bou Saada. . . . 
Barika . 



1.07 
1.5 
1.3 
0.63 
0.57 
0.72 
0.72 
0.63 
0.67 
1.6 
4.6 
4.0s 
2.4 
Ain Sefra ' 9.2 



Gary ville . 
Laghouat. 
Ghardaia . 
El Oued . . 



6.3 
309 
8.9 
53.9 



1-3 

1.8 

1.9 

1.3 

0.67 

0.64 

0.29 

0.76 

0.64 

2.3 

6.05 

5.4 

8.7 

21.5 

1.9 

4.7 

233.0 

27.7 



1.39 

1.46 

1.6 

0.5 

0.22 

0.55 

0.34 

0.6 

0.36 

1. 5 

21.2 

12. 1 
9.9 
1. 5 
2.1 
9.8 

81.4 

67.0 



1.9 

16.0 

1.3 

I.I 

0.56 

I.I 

0.58 

I.I 

0.83 

2.5 

3.9 

2.9 

5.0 

23.8 

23.9 

203.0 

529.0 

629.0 



43.3 

136.0 

146.0 

28.8 

27.1 

12.0 

15.5 

37.8 

12. 1 

7.6 

14.8 

19-5 

4.1 

124.0 

23.4 

21.0 

25.6 

482.0 



8.6 

38.1 

18.0 

5-07 

3.4 

5.2 

2.7 

14.8 

4.7 

3.5 

I.I 

8.3 

11.4 

328.0 

3.4 

25-9 

66.9 

68.6 



3.1 

1.9 

2.45 

1.06 

0.2 

0.9 

1.6 

1.4 

5.8 

4-9 

3.9 

13.9 

3-7 

14.7 

2.1 

14.2 

23.2 

46.1 



10.6 

8.9 

3.4 

1.2 

0.76 

0.35 

0.71 

1.9 

1.2 

2.6 

3.5 

5.6 

90.6 

13.2 

4.1 

154.0 

49.7 

215.0 



S.7 

3.2 

4.4 

I.I 

0.5 

0.51 

0.16 

0.8 
0.78 
1.6 
3.7 
8.3 
1.3 i 
1.2 i 
3.9 ! 
104.0 I 
225.0 
133.0 



Table 7. — Evaporation-rainfall ratio, seasonal, 1908. 



Station. 


Winter. 


Spring. 


Summer. 


Autumn. 


Annual. 


Littoral : 

Nemours 

Cape Falcon 


2.69 

1.83 

2.54 

1.0 

0.58 

0.62 

0.39 

0.73 

0.69 

1.8 

4-7 

S.9 
4.1 
1.4 
7.0 

6.0 
154-9 
68.3 


44.09 
8.75 
3.7 
7.96 
3.0 
5.0 

8.2 
1.0 
2.1 
4-05 

7.0 
6.6 
12. 5 
9.8 

73.2 
416.3 
354.0 


24.1 
58.6 
71.0 
86.4 
28.5 
117.4 

83.2 

38.3 

3.5 

0.35 

88.2 

76.0 
93.5 
67.9 
20.8 

271.6 
293.7 
485.2 


16.3 
7.95 
3.44 
1.4s 
1.48 

1.67 

6.0 

3.9 

3.6 

3.8 

9.3 
35.a 
18.S 

3.3 

64.6 
195.9 
109.5 


3-0 

3.7 

4.3 

1.8 

0.93 

X.S 

I.I 
3.3 
1.9 

4.4 

6.0 

II.O 
12.3 
II. I 
35 

17.0 
59.7 
63.0 




Bouzarea 

Maison-Car^e 

Tell: 

Ft. National 

Sidi-bel-Abb6s 

Saida 


Batna 


Tebessa 


High Plateau: 








Desert: 




El Oued 





When we reduce the evaporation-rainfall ratios of the different physio- 
graphic provinces to simple expressions we gain a comprehensive view of 

• At Touggourt, however, no rain was reported during the summer season of 1908. 



CLIMATE OF ALGERIA. II 

this important climatic factor for the colony as a whole. Thus the annual 
evaporation-rainfall ratios are as follows: the littoral, 2.5; the Tell, 3.5; 
the High Plateau, 9.4; the desert, 46.5. The relation of these expressions 
may also be given thus: i : 1.4 :s-7 '■ 18.6, for the several regions above 
given, by which we see how rapidly the aridity of the country increases as 
the desert is entered. The present custom of considering the southern 
base of the Sahara Atlas as the northern edge of the desert, in place of 
including the High Plateau, as was done earlier, is thus well grounded. 

The temperatures of the air vary greatly for the different regions, and 
usually the variation is to be directly related to the positions of the stations 
as regards the coast and the altitude. Along the coast, however, the tem- 
peratures vary even if the stations are at approximately the same eleva- 
tion. The mean annual temperature at Oran is 16.9° C. and at La Calle 
17.7° C, while a study of the January temperatures shows that a similar 
relation holds good for the entire south coast of the Mediterranean, be- 
tween Oran and Alexandria. Algiers furnishes one exception to this state- 
ment, in that the mean annual temperature is 18.1° C. On the High 
Plateau the mean temperature falls to 12.7° C. (Batna) and 13.5° (Setif). 
No records appear to have been made for the high mountains of eastern 
Algeria, although the fact that snow may remain in sheltered places as 
late as the latter part of July* would indicate that the mean temperature 
at 2,000 meters elevation is much lower than any above given. On the 
Algerian Sahara the mean annual temperature is usually higher than at 
any point nearer the coast, but even here there is considerable variation, 
depending, among other factors, on the altitude of the stations and their 
relation to the Atlas. The mean temperature is given by Engler as 20.5° C. 
for Biskra, 21.0° C. for Ghardaia, and 22.2° C. for El Golea. As increased 
temperature means increased evaporation, we have in this one factor a pow- 
erful agent making for aridity, and when this is associated with decreasing 
rainfall, as one leaves the coast region, its influence as a determinative fac- 
tor in the environment of plants is thus seen to be of great importance. 

The annual variations in the temperature of the air are very consider- 
able throughout the colony and are especially great on the desert and 
the High Plateau. At Algiers the variation is 40.7° C, at Setif it is 
48.2° C, and at Ghardaia it is 47.9° C. An annual absolute variation 
of 50** C. is not uncommon on the desert, and Engler cites a range of 
57.0° C. at Ghardaia. 

The daily range of the temperature is also considerable for all stations, 
but is especially marked in those of the High Plateau and the desert. The 
daily range as given by Engler for the former is 17.4° C, and for the latter 
20.0** C, but the range on the High Plateau may be greater than 17.4° C, 
especially during the stunmer months. For example, at Batna, in 1904, a 



* Kearney and Means, loc. cit. 



12 



BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 



range of 19.4° C. was reported in April, 20.2° C. in June, 21.8° C. in July, 
and 20.2° C. in December. Except in December, the great ranges in tem- 
perature here cited were on days when the sirocco was blowing from the 
desert; hence, the usual daily range in temperature would be much less. 
In the Tell, and especially along the coast, the range in temperature re- 
corded for any day is relatively little, although at the time of the sirocco, 
as well as during the season of drought, the daily range is not inconsider- 
able. Table 8 gives the maximum daily range for the months of 1904, for 
two stations, along the coast, including the Tell, and two stations on the 
High Plateau. The daily range reported for Batna in June, July, and 
August, 1902, was somewhat larger than the maxima given in table 8. In 
1902 the maximum daily ranges in temperature for the three months at 
Batna were 23.9° C, 25.3" C, and 24.4° C. 



Table 8.— 


-Maximum daily range in temperature, 1904. 






Station. 


Jan. 


Feb. 


Mar. Apr. May June 


July Aug. 1 Sept.' Oct. 


Nov. 


Dec. 


Algiers 


"C. 
9.0 
10.4 
ir.S 
14.0 


13.0 


"C. °C. \ °C. °C. 


°C. "C. °C. °C. 

15.0 15.4 II-2 14-0 
12.4 14.8 16.4 II. 2 
21.8 16.4 16.0 ! 19-4 
19.0 18.0 18.0 i 14.0 


°C. 
10.8 
11.6 

13.0 


°C. 
10.6 
II. 
20.2 
13.0 


Ft. National 

Batna 


13.8 
15-4 
17.0 


13.0 ' 12.4 13.0 12.8 
16.4 19.4 j ... 1 20.2 
14.0 18.0 18.0 19.0 









The temperature conditions for the j^ear 1908 will serve very well to 
further illustrate this phase of the climate of Algeria. No freezing temper- 
atures w^ere reported from the coast stations, although at the northern 
base of the Atlas of the Tell several degrees of frost were recorded. At 
Blida, for example, the themiometer registered -4.0° C. as the minimum. 
Away from the littoral at every station whose records were seen the lowest 
temperatures were zero centigrade, or below. The coldest weather was 
felt at Aflou, at the north base of the Dj. Amours, of the Saharan Atlas, 
where -11.0° C. was reported. The summer was warm along the coast 
and hot in the interior. The records of temperatiire of 23 stations of the 
Tell were seen, and of this number, at only 8 was a temperature of 40° C. 
reached or exceeded. On the other hand, at 44 out of 56 stations on the 
High Plateau and the desert, the temperatures reported are as great or 
greater than 40° C. Where temperatures below this figure were recorded 
the stations were situated in the mountains. 

The western portion of the Sahara is apparently not so hot as the eastern 
portion. The mean annual temperature for Biskra is 20.3° C. ; for Ghardaia 
it is 21° C; for El Golea it is 22.2° C; and for Touggourt it is 23.4° C. 
The mean temperature at Cairo is 21.3° C; for Suez it is 21.5° C; and for 
Djedda, on the Red Sea, it is 27.3° C. The absolute maximum tempera- 
tures in southern Algeria for as many years and for two of the most south- 
em army posts. El Golea and In Salah, are as follows: El Golea, 47°, 46.5''. 
48^ and 49.2° 0.; In Salah, 50.0°, 49.2°, 50.2°, and 48° C.; at Ouargla the 



CLIMATE OF ALGERIA. 



13 



maxima are 50.2°, 51°, 52°, 49°, and 48.4° C. On account of the fact that 
in the western Sahara at these stations in mnter there are usually freezing 
temperatures, the yearly range of temperature is 50.0° C, or over. The 
greatest range reported for the western Sahara is that for Ghardaia as 
given by Engler, namely, 57°, from -7° to 50° C. At Timmimoun, 1904, 
the range was from -3.0° to 53.1° C, or one of 56.1° C. The extreme abso- 
lute daily range in temperature on the desert appears not to exceed that 
of certain stations on the High Plateau, although, as shown below, the 
temperatiu-e variations on the desert may be much larger than the records 
indicate. At Laghouat and at Ghardaia the thermometers which I exposed 
showed a daily range of from 10.5° to 12.5° C. only. The instruments 
were placed on the outside of buildings, and usually on the second story. 
As a contrast to this observed diurnal variation, an opportunity was given 
to take temperatures on the open desert at a time when the days were 
fairly warm and the nights were rather cold. The place was between Toug- 
gourt and Ouargla. At 3 o'clock on the afternoon of November 26, 1910, 
the shade temperature at the place in question was 23° C. During the 
night the thermometer registered -1.7° C. as the minimum, thus showing 
a drop of 24.7° C. in something over 12 hotirs. Table 9 gives the extreme 
daily range in temperature for three years observed at the stations named. 





Table 9. 


— Absolute daily 


range in temperature. 






Station. 


Jan. 


Feb. 


Mar. 


Apr. 


May. 


June. 


July. 


Aug. 


Sept. 


Oct. Nov. 


Dec. 


In Salah 

Ouargla 


° C. ° C. 
21.6 23.0 
20.8 1 25.4 


° C. ° C. 
24.4 24.6 
24.0 25.0 


22.0 
27.0 


°C. 
23.2 
26.0 


°C. 
23.4 
26.0 


-c. 

22.0 
27.8 


°C. 
29.0 
24.6 


° C. 1 °c. 

20.0 23.4 
23.0 1 20.0 


"C. 
22.6 
23.8 



A further examination of the maximum temperatiu-es shows certain cli- 
matic features of interest and of great importance as factors in the environ- 
ment of the desert plants, especially the high average maxima and the 
large amount of heat received in the desert, as indicated by a summation 
of the maximal temperatures. That the greatest daily temperatures must 
be high is indicated by table 10, which gives the average maxima for three 
to five years at three typical desert stations. 





Table 


[0. — Average maximum temperatures. 








Station. 


Jan. 


Feb. 


Mar. 


Apr. 


May. 


June. 


July. 


Aug. 


Sept. 


Oct. 


Nov. 


Dec. 


Ouargla 

El Golea 

In Salah 


°C. 
21.9 
23.0 

27.4 


"C. 

I8.3 
25.8 
30.1 


°C. °C. 
30.9 37.8 
35-6 27. S 
37.2 41.0 


"C. 
41. 1 
40.9 
43.4 


"C. 

47.1 
44.4 
47.6 


"C. 

49.4 

47. s 

44-3 


47.7 
46.0 
47.1 


°C. 

44-3 
43-8 
45-9 


"C. 

40.0 
36.7 
41.3 


"C. 
31.0 
29.9 
37.0 


"C. 

2S.0 
32.4 
27.1 



The maximum temperatures show that the total amount of heat re- 
ceived on the desert, as compared to that received in the climatic pro\dnces 
nearer the sea, is not only great, but also that the amount is variable on 



H 



BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 



the desert itself, one station receiving much more heat at certain times of 
the year than another station. The total heat for each station is arrived 
at by adding np the daily maxima for the midseasonal months, January, 
April, July, and October, and dividing by the number of years whose records 
were consulted. The amounts given in table 1 1 are the averages for three 
to four years, for three desert stations and for one station in the Tell. 

Table i i . — Sums of the daily maximum temperatures. 



Station. 


January. 


April. 


July. 


October. 




°C. 
439 
641 
570 
230 


°C. 

476 

1,027 

909 

470 


°C. 
1. 135 
I.4S5 
1.444 
697 


°C. 

668 

1,121 

923 

564 


In Salah 


Ouargia 

Ft. National 



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 im- 
mediately south of the Saharan Atlas, latitude 33°48', and at an elevation 
of 780 meters. Ouargla is approximately 200 miles south of the moimtains, 
latitude 3i°S5', and altitude 150 meters. In Salah is in the midst of the 
western Sahara, latitude 27°! 7', and about 300 meters above the sea. 
Fort National Hes in the Tell about 30 miles from the sea, and at an alti- 
tude 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 ther- 
mometers were used. They were placed in a horizontal position in fixed 
tubes which were about 30 cm. in length. Precautions were taken to prop- 
erly insolate the instruments. The depth was 15 cm. 

Table 12. — Soil and air temperatures, Ghardaia, July 2-1 1, 191 1. 



Date. 


Soil. 


Air. 


Maximum. 


Minimum. 


Maximum. 


Minimum. 


July 2 
July 3 
July 4 
July s 
July 6 
July 7 
July 8 
July 9 
July 10 
July II 


°C. 
36.0 
36.0 
36.0 
36.S 
33-7 
36.0 
36.0 
37.0 
37.0 


"C. 
31-0 
31.0 
31.0 
31.5 
32.0 

32. S 

32.5 

32.5 
33-0 


° C. 
41.0 
41.0 
41.0 
41.0 
41.0 
40.0 
38.0 

40.0 


° C. 
21.0 
22.0 
23.0 
25-5 
25.0 
26.0 
26.S 
25.0 
24.0 
23.0 



An examination of the meteorological reports for Algeria shows that the 
direction of the prevailing winds varies considerably, although the varia- 
tion is possibly greater near the coast than in the interior. The ^inds un- 



SOME CHARACTERISTICS OF VEGETATION OF THE TELL. 1 5 

doubtedly play an important r61e 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 ^vinter 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 con- 
secutive 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 rela- 
tive 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-Hke 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. 



1 6 BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 

Very much the same conditions greet one when he arrives in Algiers, ex- 
cept 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 beau- 
tiful city of Algiers contain fine plantations of foreign trees, such as eucalyp- 
tus, 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 (JPinus halepensis) 
from lower altitudes; there are junipers and oaks, am.ong 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 char- 
acter 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 Caree . . . 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, ascend- 
ing gradually alongside the Oued ChifTa, he sees, among other forms, ex- 
tensive areas of dwarf palm, doum (Chamcerops 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 



SOME CHARACTERISTICS OF VEGETATION OF THE TELL. 1/ 

doum bales were observed being vigorously driven marketward by their 
small boumoused 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 gam- 
boling 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 scatter- 
ing 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 vegeta- 
tion, 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 siiher), which grows 
under more moist conditions, as between Tunis and Constantine, or be- 
tween 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 bollota), juniper (Juniperus oxycedrus), and "dherou" {Pis- 
tacia 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 forma- 
tion 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. 



1 8 BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 

THE FORESTS OF ALGERU. 

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, cer- 
tain 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 siifficient abundance to constitute forests proper. The leading species 
are, among the conifers, Cedrus atlantica and Pinus halepensis. The juni- 
pers 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 inixed 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; jumper 
(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, ma}^ be determined. In altitudi- 
nal 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. hisitanica 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 alti- 
tude — probably of the first rank should be considered the rainfall and the 
temperature, which are affected by the altitude. In the case of the dis- 
tribution of the cork oak, however, the character of the soil plays an 
important role. 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 ex- 
plained. For example, in the upper limits of its range, Pinus halepensis 
appears chiefly on southern slopes, as on Mount Gomo, 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 



THE FORESTS OF ALGERIA. 1 9 

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 
Gomo 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 wovdd perpetuate the best-liked varieties. 
It may be remarked in passing that the seeds of the pine are also in com- 
mon use among the Arabs as a food, although not employed so generally 
nor in so many ways as the acorn. 

The cedar (Cednts 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 Aures. The forest seen was that near Batna, 
near the western base of the most important range in Algeria, the Aures. 
Somewhat below the lower limit of the Batna cedar forest is an open forest 
of oaks {Quercus mirheckii) , Junipenis oxycedrus, and /. phcemcea, mingled 
with which are shrubs suggesting those of the desert, such as Acanthyllis 
numidica and Retama sphcerocarpa, 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 {Arceu- 
thohiumoxycedri). 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 strag- 
glers in the dry wash at the north base of the mountain on which the forest 
is situated. In part these trees were shapely, mth 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 



20 BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 

first characterized, with widely reaching lower branches and slender sum- 
mits. 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 i 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 CheHf, 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 bound- 
ing 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 tama- 
risks, and on the plain not far from the oued are a few specimens of Zizy- 
phus 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 



BOGHARI TO LAGHOUAT. 21 

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 Qtiercus balloia, 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. Jtmipenis 
oxycedrns and /. phcenicea 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 Nocsa 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 fiat 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, 
"situees 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 dis- 
tribution of the species is apparently that of rainfall, reacting in this respect 
very like plants with storage organs, avoiding alike regions where the rain- 
fall 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, command- 
ing 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 



22 BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 

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 north- 
ern 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 inconsider- 
able, 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 moun- 
tains 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 theapproachto 
Laghouat, written about 1 860, 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 hori- 
zontal. . . . Our next day's ride was by a base of a continuous chain of steep ridges. 



LAGHOUAT. 23 

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. Turn- 
ing around to our left and crossing the dry channel of an evaporated and aged "Wed," 
we liad 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 open- 
ing 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 Hes 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 south- 
west, 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 men- 
tioned 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 be- 
cause 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. 



24 BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 

THE OASIS OF LAGHOUAT. 

The oasis of Laghouat is situated on the Oued Mzi, the upper portion 
of the Oued Djedi, one of the most important oueds of Algeria. The Oued 
Djedi runs in an easterly direction from Laghouat, receiving many tribu- 
tary oueds en route, by a rather long covu-se to the great Chott Melrirh, 
which is southeast of Biskra. Like other desert rivers, the Oued Djedi is 
dry most of the year, but is occasionally filled to overflowing with a rush- 
ing flood, which is of great erosive power and may be very dangerous to 
the traveler. Above the town of Laghouat, where the Oued breaks through 
the last pass of the Atlas, the flood-plain is narrow, but upon leaving the 
pass the plain widens until in the immediate proximity of the town it is 
about 1.5 kilometers in width. On either side of the flood-plain stretches 
the arid plain (hamada), usually stony, but near the mountains covered 
with low, slowly moving sand ridges. To the south of the oasis, the arid 
plain merges into the topography characteristic of the region of the dayas. 

The portion of the oasis devoted to the cultivation of date and other 
trees, and to gardens, is about 3 square kilometers in size, but arable land 
extends above and below the town, so that outside of the oasis, as delimited 
above, there are about 6 square kilometers, all of which have at times been 
imder cultivation. The last referred to is the flood-plain of the oued and 
is used mainly for growing barley. By the edge of the oued, or along the 
irrigating ditches, are several characteristic species of plants, which may 
point to the character of the primitive flora; for example, willows, oleander, 
and Tamarix, with a few palms. The betoum {Pistacia atlantica), which 
must surely have been an inhabitant of the oasis formerl}^ is now appar- 
ently wholly absent. The species just mentioned are to be found between 
the town and the pass above; but below the oasis, owing to an apparently 
poorer water-supply, there are fewer large species. Among those found 
are a few specimens of Rhus oxycantha and Zizyphtis vulgaris, and it was 
probably below the town that the betoum was to be found in earlier times. 

The oasis is under intensive cultivation (see fig. i). There are about 300 
gardens, each bounded by mud walls, and often separated by pictiu-esque, 
meandering lanes. The plant life, almost wholly introduced, is luxuriant. 
In some gardens the effect is tropical, where vines reach from tree to tree, 
making a canopy nearly sun-proof and separating the spreading tops of the 
palms from the wealth of shrubbery and herbaceous plants beneath. First 
among the trees of the gardens, in numbers as well as in economic impor- 
tance, is the date palm, of which there are said to be about 30,000. Although 
this is small in comparison to the number of date palms at Ouargla, Toug- 
gourt, or the Oued Rirh, the dates are of great importance to the dwellers 
at Laghouat, where the products of the gardens are almost all consumed. 
The living tree provides shelter against the intense heat and light of the 
desert, and the dead leaves constitute an important source of fuel in a 
land where fuel is extremel}^ hard to obtain. The flesh of the date fruit 
is eaten by the Arab and the cracked seeds are given to the camels. With- 



LAGHOUAT. 25 

out the date a continuous occupancy of a remote oasis by the Arab is 
clearly impossible. Besides the date palm fruit trees of other kinds are 
abundant, among them the apricot, fig, mulberry, peach, pear, and orange. 
The pomegranate and the table grape are also very generally grown. The 
lowest story of the vegetation of the gardens is composed of garden vege- 
tables, such as artichoke, bean, carrot, melon, pea, potato, squash, and 
radish. Among the ornamentals one sees roses, asters, and chrysanthe- 
mums, and occasionally very luxuriant cannas. One or two parks contain 
interesting introduced trees and shrubs. We recognized among the trees 
Atlanthus, Eucalyptus, umbrella, plane, poplar, pine, cypress, ash, locust, 
willow, and St. John's tree. The Barbary fig (Opuntia ficus indica) is also 
common, but does not stray away from the best-watered situations. 

THE PLAIN. 

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 sm.all stones and pebbles, 
gives the impression of total barrenness. Not a tree, shrub, or herb ap- 
pears 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 evi- 
dence of plant Hfe. 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 
(Acanthyllts tragacanthoides) , adhidh {Zollikojeria sptnosa), rempt {Haloxy- 
lon articulatum) , and drinn {Artistida piingens); Acanthyllts is perhaps the 
m.ost 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. 



26 BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 

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 
1 6 by 1 6 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 speci- 
men 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 groimd 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 gen- 
eraHzed* 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 campesiris were growing in a Httle 
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 

* The Root Habits of Desert Plants. W. A. Cannon. Carnegie Institution of Wash- 
ington Publication No. 131 191 1. This paper gives a descriptive classification of the 
main root-types iti the deserts of the southwest, in which such a root as found in Acan- 
Ihyllis is called generalized, in distinction to roots like those of most of the cacti, or 
Zizyphus, the former having a system wholly superficial and the latter a system wholly 
deeply placed, as specialized. The specialized root-.systems appear to be so fixed in 
character as to be not easily changed, while the generalized type is flexible. It will be self- 
evident that the type of root-systems may be of great importance in determining the 
local distribution of a species. 



LAGHOUAT. 2/ 

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 endur- 
ing very arid conditions, is unarmed, and is much eaten by all herbivorous 
animals. The plant mil 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 tj'^pe.* 

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 b}'- 
Tilrempt and Ghardaia, as well as between Ghardaia and Ouargla (Gan- 
tara) . 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. vSand 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 indi\dduals, 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 fre- 
quently happens where there are moving dunes, the passage of the dune 
greatl}^ 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. Acanihyllis tragacan- 
thoides, a plant typical of the plain, was found to sur\'ive the passage of the 
sand, although changed in appearance in a characteristic manner. It \%'ill 

* Compare the root-system of H. scoparium at Biskra, p. 64. 



26 



iiO'/AMCAL i-LATURES 0\ liiL ALOERIAN SAHARA. 



be recalled that th' 
ing from tlie root- 
winda, the lateral.: 
that a plant, alrea: 
the heaping up of 
as the sand er 
dune has pa«/ 
fJie depth of t? 
that Acanthylli 
that the rat>» o . 



v^ ^-onnsting of severe shoots, spring- 

the ground, and a root-system in 

-'i aKke well developed. In order 

... .aintain this general relation during 

:n root must grow at the crown as fast 

at happens, so that, when the 

f-lf-vated for a space equaling 

ore. From the probability 

'; Ties are low, it follows 



within 3 



.-laran /. 
"^.^asis. llns rani^ 
* Higher mour 
'otnads are 
• theoa 



S».«''1 i': 



jrth of Las^iooat, 

Tountains) is not 
*', '■" ••"-^. and 

;.igh, 

i, and it 
■—face, 



t,;. 

A 
froiT; 



J, nhh/Ai'f/h T. r.daril. 

"? M«-/ijr)t,.';; n. One was in a 

en n/ule '/> J.;; ?' :-;t,, from the Hi^'h 
.'J I 'icii; thui va^jcjjxmI 

flocks. The phy.y ■■'. ■■:•.. 

ifjnsi. As one a; .-om 

irifc iixxTtuA^ oi i>lantK grows leas unlil oj. 

^'3t on attaininj^; the crest they (\n\'./..j ... . :■.. .-. ... . 

:X in the lan/l«jcape. In faet, the flora of the northern 

': tl'ie fioil conditions are rcb' : (^.frablr;, i:^ much 

retain or the dunes. Had the ... ..- . ix*n of good size 

(.f:i\:j.iu hjfiix (/n the nrjrrth r;Iryf>e of the Nomad Mountains, not far 
th^; Iju:^ through v/hich the Oued Mzi goes, was selected for making 





■;'jujai anr: 


J^ 




t/. 




t: 


liie 


<■, 


• r;. 



*Tbe OKWt ttriking change in the general character of the v^etation which the 
trard^' notices af he goes from tiie less arid to th« mr/r*-, mid portiot^fottthem Algeria 
if its decrease in amount. ThU occurs through dwar^na effect* of whatever cause and 
throujg^ a decreaie in the number cA in/lividuaU. Within certain limits the results 
observed are to be attributed mainly to the first of these, since there is often a sur- 
prittngly large number of perennials on any given area. But in other and more intensely 
arid regions (^ portions of thA Arabian -Bg/ptian daiert, and indeed a limited area on 
the bamada between Ghardaia and Ou;ir;{La) plants are wholly wanting. Whether such 
is generally the case on the t'sh or the YnxmaAa, fjarther south in southern Algeria is not 
known. 



LAGHOl'AT. 29 

a census of the platU popul;\iioi\. Hero iho number of individuals, as well 
as their size, showed that the nioistuix^ relations were good as conipariHi 
with those of the plain. On an ai\\i 16 meters squan^ 433 li\-ing pereinu;Us 
weiY fotnul. n\ainly of the following spevMes: Acatilhvllis tnj^i}i\itii}u>t\{fs. 
Asparagus sf>iftosa, Dcvcrra scoparia, and Zollikofetia spinosa. The most 
numerous. Zollikofetia, was represetiled by oo individuals. The general 
character of the habitat and the plants is sutlicicntly well shown in lig. 8 
and does not need further mention in this place. 

KFFKCTS OF llRAZINC, ON VKC.KTATION NKAR I ACUOt'AT. 

It is generally recognized that a poteitt inlhict\ce is exerted by man. 
and the lower atiimals, in shaping the llora of at\ arid ivgion, not only ns 
rcgatxis the kind and nuti\ber of plants, but also as eoneenis certain of the 
leading characteristics of the plants themselves. The actiot\ is largely sudi 
as brings about a siu-vival o{ the "useless" fonns. si"* that wc do wol ktiow. 
froin the plants wc meet in the desert to-day. how many or what kinds of 
plants it might support. It also t\iay be true that no desert shows the mod- 
ifying ellects of the causes suggested motv than the northern Sahara. 

The gazelle (Gasella donas) is the leading wild aninial preying upon the 
desert plants in the niM'thcrn Sahara. It is ftvqucntly seen by (he traveler 
to-day and was present in large numbers no loi\gcr ago than 50 years i,Tris- 
tram). It is said by the Arabs to teed on the fresh shoots anvl leaves of 
mat\y species o( shrubs aiul trees, especially the betoum {l''istaoia atlaniica), 
as well as on the antuial vegetation for the ivlativcly short, period when it 
is to be had. Other species of ga.'.ellc. ac(.xM"ding to Tristran\, range farther 
to the south. Other herbivorous animals o( the ivgion are hares, antelope, 
mtnttllon. and bubale. The moiilllon. at the time oi Tristram's visit, was 
"far from uncomiuiMi througlunit the wlu>Ic o( the mountain ilistricts, 
whether winnlcd or bare," but the bubale. "the wiKlesl o( the wild game 
o'i NiM'th Africa." appears not to go \\ov[\\ o\' the Owed Rirh, while its home 
is farther .^outh. It is impossible to know the imnibcr v( wild .mimals 
subsisting on native desert vegetatiiMi. but the list given, which might be 
cxtcuilcd. snggcsts that it is by no means small. Althongh (he populativMi 
(>f wild hcrbivoiiMi;; animals is at pic:;ci\t considerable, it was probably 
nnieh greater a few years ago. the dcctvasc being due, as Tjislram says. 
nol so much to the gtvatly increased population as to (he moiv ellicient 
weapons ns(\l by the .Arabs in hunting.* 

* rrisliiuu remarks tl\at it " soonus lliat ll\i' lar>;i>r wild aniiuals liavo hoon rapivlly 
doort'asiii>; in uuiuIums and arc in pn.Kv.-^s of spivtiv cxtiivclivii. l>f. Sliaw. 150 yoai.-i 
siiioo. ciuiMKMato.'^ in his travels . . . live sinvio.'^ i^f rtii\>inants. wlueli t"n>m liis doserip- 
tions must ho llio lMil>alo, tlio aovidud y^r wild slirrp, tlio addax, and tin- jj.u-rllo, «s wdl 
ns the Stan- . . . As tlio population has not imivasod. hnl ratlior ivln<);radrd. we can 
only suiniiso tliat tlio snlistilntiim o( tlio Hint and slool ^;nn for tlio nialohlook of (ho 
Modonin . . . has hocti fatal in its tosults to jdl lar>;or Kiuuc." It may ho nMn.nkod tliat 
tho I'^ronoli iniposo snoh lostriotions oi\ llio Aiah as ro^anls the ohacaotor of tlio j;nns lio 
may nsc (oiily llio aiiuy antl oortain olVioials of tho K*'Vorniuont ompUnin>: modnn 
arms) that for tlio ivj;ion visitoil Tiistrjun's do.'^oiiption holds fairly well for to-i!av. 



30 BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 

Laghouat has been inhabited by the Arabs continuously for about 1,000 
years, during which time the oasis and its en^drons 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 pastiires, 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.* 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 num- 
ber 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-supplJ^ 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 t^ie 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; 

*Statistique G6n6rale de I'Algerie, 1908. 



FROM LAGHOUAT TO GHARDAIA. 3 1 

for example, the betoum {Pistacia atlantica) probably formerly either grew 
in the oasis of Laghouat or near by, since it was fonnerly 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 day as south of Laghouat, where it is the only arboreal 
species of the region. 

From what has been said regarding the large numbers of domestic ani- 
mals 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, distaste- 
ful, 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 tra- 
gacanthoides) , 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* 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 extermi- 
nated 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 dip- 
ping 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. lo and 1 1 .) 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 

* Un voyage botanique au Sahara, Bull. Soc. Bot. Belg., 1898. 



32 BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 

of western America. On the plain in the northern portion of the daya region 

the following may be observed : * 

Echinops spinosus. Citrullus colocynthis. Teucrium polium. 

Acanthyllis tragacantholdes. Artemisia herba-alba. Aristida obtusa. 

Thymelaea microphylla. Artemisia campestris. Stipa gigantea. 

Peganum harmala. Haloxylon articulata. Noasa spinosissima. 

Euphorbia guyoniana. Anabasis articulata. Astericus pygmaeus. 

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 por- 
tion 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 
stratimi 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 con- 
siderable 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 cis- 
tern was empty when we were there. These observations are given to show 
imder 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 ad- 
verse conditions. The altitude of the daya is about 600 meters. 

As one crosses the plains in the vicinity of Tilrempt he notes the scanti- 
ness 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. 

* Massart, loc. cit. 



FROM LAGHOUAT TO GHARDAIA. 33 

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 articu- 
latum, 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 sur- 
prising mmibers. 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 fig- 
ure. Numerous specimens of jujube are also scattered through the daya, 
with some Peganum harmala and Francceuria 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 
1 5 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 fotmd 
4.56 meters in circumference, another 4 meters, while a third measured 
3.36 meters. All measurements were made i meter from the surface of 
the ground. No betoums, however, were seen to have developed in a per- 
fectly normal way, and this observation appHes not only to Tilrempt but 
to all other dayas seen, but they were disfigiu-ed 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 exist- 
ing 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 wotild be exterminated 
if it were not protected by another plant, namely, the jujube. f The char- 
acter 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 

• Joan's Guide de I'Alg^rie et de la Tunisie. 

t Massart, loc. cit., p. 314, suggests that the Sahara may be gradually becoming more 
arid and says that as a result the betoum is becoming more and more rare and may become 
e.Ktinct. He says "L'extinction du Pistacia atlantica pr^sente le caract^re, tout k fait 
exceptionnel, d'etre uniquement I'effet du climat." It will appear from what is said in 
this study regarding the efifects of grazing in general, as well as the especial effects on 
the betoum, that if the betoum is becoming extinct the sole cause, or perhaps the main 
cause, is not the adverse climate. 



34 BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 

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 pro- 
tection 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, 19 10, 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 stirvival; with relativ^ely 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 



FROM LAGHOUAT TO GHARDAIA. 35 

low and with flat summits, but as the distance from the daya region in- 
creased, 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 con- 
dition 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 continu- 
ously 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 con- 
sider the chebka a barren desert, absolutely devoid of plant life; but closer 
inspection dispels this illusion and reveals the presence, in the more favor- 
able 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, Petama spherocarpa, 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* 

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 \^dder. 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 fruticosuni, Arte- 
misia herba-alba, Ononis angustissima, Linaria fruHcosa, Antirrhinum ramo- 
sissima, and Haloxylon articulatum (Massart, loc. cit.). Peganum harmala 

* Dr. Charles Amat, Le M'Zab et les M'Zabites, p. 70, gives a somewhat higher 
temperature for the rocks of the southern Chebka, placing it at 90° to 100° C, or even 
higher. 



36 BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 

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, diver- 
sified 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* as "le ddsert par excellence, la vrai desert . . . les 
grandes plaques pierreuses ind^finies 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 ex- 
tends 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 simk 
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 east- 
ward and at last lies but little below the general level of the coimtry. 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 ;t but it has 
probably been not less than nine centuries.J 

• Les Oasis du Souf et du M'Zab, La G^ographie, 1902. 

t Foureau, d' Alger au Congo par le Tchad, 1902, mentions having met with indica- 
tions of early settlement of the Sahara by people now forgotten, and whose tombs, 
inscriptions, and other remains, were well known by his Touareg servants, although 
not at all understood by them. So far as I have learned, however, it is not supposed 
that the region of the M'Zab was inhabited before the coming of the Beni M'Zabs. 

t There are seven cities of the Beni M'Zab, of which five lie in the M'Zab Valley, 
close to one another. These are El Ateuf, Ben Noura, MeHka, Beni Isguen, and Ghar- 
daia. In the pre-French times these cities were bound together in a confederacy with 
Ghardaia as the capital. The M'Zabites are at present, and probably always have been, 
a peaceful trading folk. They are heterodox Moslems. In an early time they aroused 
the antagonism of their more warlike as well as more orthodox Arab neighbors of the 
Tell, who drove them away from the coast region, and again from Ouargla and other 
places settled by them, until safety was at last secured in the eleventh century in the 
" inhospitable Chebka." Palm gardens were estabUshed which for centuries have been 
irrigated laboriously by very primitive methods, and the inhabitants have accumulated 
wealth in flocks and by barter. The relatively large population (there were 92,761 
inhabitants in 1908), the really great number of domestic animals, and the great length 
of time which the region has been occupied, are all factors of importance in bringing 
about a modification in whatever way of the primitive flora. 



GHARDAIA. 37 

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 sta- 
tionary 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 thresh- 
ing 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 deflned perhaps, of approximately the same 
thickness, and \Adth 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 stratimi projecting as a shelf, sometimes as large 
as 2 by 4 meters in extent . When the shelving banks break they remain prac- 
tically intact, partly buried by the sandy floor of the oued. (See fig. 17.) 



38 BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 

Along the sides of the valley, and at a distance more remote from the 
oued, there are occasional washed-out areas, really box canons, 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 waterwom 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 i 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 directh'- 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 gar- 
dening is practised and the fruits of the soil, although won with great labor, 
are nevertheless not inconsiderable.* 

Perhaps the most palms are to be found about 2 kilometers above 
Ghardaia, where they are so abundant as to forni a small forest. Here, 

* In 1908, according to the Statique gendrale de I'Alg^rie, there were cultivated in 
the territory of Ghardaia 572,114 fruit trees, among which were: almond, 5,850; fig, 
101,722; date palm, 209,898; other sorts of fruits, 211,761. There were also 17,268 hec- 
tares of grain under cultivation. 



GHARDAIA. 39 

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 grapc-vdnes which reach from one })alm-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 di\dded into diminutive fields, frequently not larger than i 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 
heav^en" 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 debris, 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 accumu- 
lated 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 care- 
fully examined with results which are summarized in the following para- 
graphs. 

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 v^alley, 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 sim.- 



40 BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 

ilar, a larger number of plants were found, including, among other species, 
Aristida sp., Centaurea pubescens, Deverra scoparia, Fagonia bruguteri, Pega- 
num harmala, and Teucrium pseudo-chamcepitys. A census of plants was 
taken, where the individuals were most numerous, with the following result : 
On an area i6 by i6 meters there were 330 living specimens. The three 
dominant species were Aristida sp., Deverra scoparia, and Helianihemum 
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 de- 
pression 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 de- 
pression, 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 coiuitry 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 Aris- 
tida 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 Hving perennials were found with nimierous 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. 



GHARDAIA. 4I 



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 occm* on the walls of the valley or on the mountains, and nowhere 
else. These are the "kabar," Capparis spinosa, and one or more crusta- 
ceous lichens. (See figs. 2 2 and 23 .) The kabar is a large shrub, i to 2 meters 
high, which bears persistent and fairly large leaves. The shrub is uneaten 
by animals, owing to some disagreeable flavor,* 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 foot- 
hold. 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 YnW 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 sur- 
prising wealth of vegetation. Such conditions were seen between Ghardaia 
and Ouargla and will be specially noted on another page. 

At present no trees occiu: naturally in the valley in the vicinity of Ghar- 
daia 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 dis- 



* We were informed by our Arab attendant that the kabar, particularly the fruit, 
made such animals as ate it insane. The spicy flavor of the plant might otherwise be 
distasteful to animals. 



42 BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 

tributed 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.* Like its relative in the south- 
western 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 essen- 
tially the same distribution and appearance it had before the country was 
inhabited. It is interesting to note that Pegammi 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, show- 
ing 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 chrysocmnoides, Mluropus 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 seciire 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 occiir in the region natvu-ally. 
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 

* Fitting (Die Wasserversorgung und die osmotischen Druckverhaltnisse der Wiisten- 
pflanzen, Zeitschr. f. Bot.. 4, 209-275, 191 1) states that water-storage tissue is wanting, 
that in addition to being large, the leaves are much divided, without trichomes, and 
provided with thin cuticle. The stomata are fairly large, rather numerous, and not 
sunk. The leaves transpire rapidly and wilt soon after being removed from the stem. 
The osmotic pressure of the cell-sap of the leaves was found to equal 35.3 to 64 atmos- 
pheres, from which it is assumed that this plant, like others growing under desertic 
conditions, has a root cell-sap of great osmotic pressure, which permits it to extract 
water from a fairly dry soil or at a rather rapid rate. But neither at Biskra nor else- 
where, so far as I know, does Peganum grow where the conditions are extreme, as might 
be concluded from the habit of the plant as given above. 



GHARDAIA. 43 

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, with- 
out disturbance, must be in essentially the same condition as regards the 
soil and water relations, which would be m.ost affected by the fact of inter- 
ment, that they were in 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 canons; 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 iteslf . 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 por- 
tion the drifting sand has obHterated 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 Hal- 
oxylon articulatum and Henophyton deserti, both species eagerly eaten by 
animals, as well as Deverra scoparia, Lilhospermum callosum, Zilla macrop- 
tera, and Helianlhemum sessiliflorum; also grasses and other plants v\^hich 
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 abund- 
ance, 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, Eckinopsilon 
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 Cap par is spinas a. 
4 



44 BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 

The cemetery situated wholly on the edge of the plain has an unexpect- 
edly 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 establish- 
ment 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 modi- 
fied 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, Tam- 
arix, and others seen later. However, Haloxylon articulatum, although 
eaten by all animals so as never to develop in a normal manner, is surpris- 
ingly 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 ; exami- 
nation of the roots in the field was therefore carried on mostly in the vaX\eY> 
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 direc- 
tion. (See fig. 33.) Teucrium pseudo-chamcepitys, Centaurea puhescens, and 
Salvia CBgyptica, all from the hamada to the north of the M'Zab Valley, 
have pronounced main roots. A similar type of root was seen in Zolli- 
koferia resedifolia and Fagonia hruguieri 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. 



GHARDAIA. 45 

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.* 

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 pres- 
ence 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 undetennined 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 hori- 

* It has already been shown that the number of days on which rain may be expected 
to fall each year is greater at Laghouat than at Ouargla, and probably at Ghardaia also. 
According to reports, the rainy days at Laghouat vary from 20 to 84 (seven years' 
observation), with an average of 49 each year. The average number of days on which 
rain falls at Ouargla is 14.2. The amount of rain at Laghouat is 200 mm., at Ouargla 
90.2 mm. It would appear, therefore, that the average rain at Laghouat is less in 
amount than the average rain at Ouargla; or, in other words, it points to the torrential 
as being the type of the desert storm. Since, other things being equal, the greater storms 
would penetrate the ground the most deeply, we may here have an explanation of the 
emphasis at Ghardaia on the tap-root as against the generalized root as the type of 
the root-system. 



46 BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 

zontal 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 deepl}'', but reach rather widely. They are of the 
generalized type,* similar in many ways to the root-system of Covillea tri- 
dentata 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.f 

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 sepa- 
rated. The first specimen studied was one of a colony of a half-dozen whose 
habit of growth is shovm 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 hori- 
zontally 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. 

* The Root Habits of Desert Plants, /. c. 

t Compare the root-system of the species at Biskra, p. 64. 



GHARDAIA. 47 

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 coniimi 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 Phelypcea violacea, which 
was seen at Biskra and will be described later. 

In the habitat of Pegannm, and a few meters distant, was found a speci- 
men 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 de- 
scribed by Schimper, in "Plant Geography," as follows: 

A cucurbitaceous plant resembling our cultivated pumpkin, and its long, juicy, rel- 
atively 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. 

Wliiie the description of Schimper is a good one, it conveys the idea of 
much greater luxuriance of growth than was observed for the species at 
Ghardaia. As a miatter of fact, the leaves of this plant are small and much 
dissected, and the fruit is the size of an orange. How deeply the roots 
penetrate the ground, or their length, was not learned, but a very striking 
characteristic of the root is its fleshiness, which is shown by fig. 37, and the 
ability of the species to successfully withstand drought may lie in the fact 
that it is thus provided with a very well-developed and very well-protected 
water-storage organ, as much as in having a great length of root. Citrullus 
occurs typically where there is considerable depth of earth, especially close 
to oueds, although it is rarely to be found on the plain and only where the 
soil is deepest. In the latter habitat the possibility of a permanent con- 
nection with a perennial water-supply is without question excluded. The 
species is rather to be considered one of the forms, rare to the Sahara, 
which possess a water-balance, and which has the power of storing sufficient 
water during the widely separated rainy seasons to last it during the period 



48 BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 

of drought. It can be pointed out here that plants having hypogeous water- 
storage organs have a very different relation to the climate of the desert 
than such as have such organs above ground. The inclosing soil is a pro- 
tection, nearly perfect, against drjdng. Where the soil is removed the 
protected parts quickly become dry.* Given two species, both having 
water-balance, but one with the storage epigeous and the other hypogeous, 
other conditions being equal, the latter should survive imder more arid 
conditions than the former. It is rather surprising, therefore, that there 
are not more of the latter type in the Sahara. 

A few measurements of the root of a typical Citrullus from the M'Zab 
Valley will give a concrete idea of the water-storage capacity of the species. 
A specimen growing in the oued near Ben Isguen was selected for examina- 
tion (see fig^ 37); it had a luxurious shoot and several fruits. The shoot 
was found to arise from a large and aged root 26 cm. in diameter at the 
crown, but tapering rapidly, it was only 12 cm. in circumference at a point 
14 cm. beneath the surface, where it forked, giving off one branch which 
was 1.7 cm. and another 1.8 cm. in diameter; several smaller ones took 
their origin close to the surface of the ground. In its general appearance 
the main root of Citrullus is very like that of Cucurbita digitata, which 
grows on the domain of the Desert Laboratory and in a similar habitat. 

Up to this point the plants whose roots have been described were found 
growing where the soil was favorable to a fairly normal development, but the 
soil of the valley is not all of this character, and where hardpan is present 
the substratum is often extremely hard and, one would think from inspection, 
impermeable to water as well as impenetrable to roots. In such habitats 
the number of individuals and also of species is very naturally limited. 

About 2 kilometers west of Ghardaia is an area where the hardpan reaches 
nearly or quite to the surface. Here Peganum harmala is to be found, since 
its generalized type of root-system is capable of not a little variation, 
adjusting the species to a variety of soil conditions not otherwise possible. 
Associated with Peganum was a single specimen, of dwarfed and badly 
eaten form, growing out of the hardpan itself. The position of the plant 
was so unusual that its root-system was in part excavated. The form, an 
undetermined chenepod, was found to have the exceptional fonn of root, 
thus proving the rule just suggested, for it had a well-marked tap-root. A 
gnarled main root was foimd to take a zigzag course through 27 cm. of 

* In the vicinity of Tucson (see The Root Habits of Desert Plants) is to be found a 
slender-stemmed Opuntia whose roots are fleshy and are placed within 2 to 4 cm. of 
the surface of the ground. It has been observed that if the roots are examined in the 
midst of a dry season, as in June, they are gorged with water, but if the soil is removed 
for a few hours they become shriveled. A similar habit was seen in another species of 
the same genus. Two other genera of the cacti from the Tucson region have the water- 
storage organs wholly or partly protected by the soil. In Cereus greggii the subterra- 
nean portion forms an organ 15 to 30 cm. in diameter, and in the other form the fleshy 
subaerial stem is partly drawn under the surface of the soil, so that only the flat upper 
surface is visible. 



GHARDAIA. 49 

hardpan to the softer stratum beneath. The root did not follow a crack, 
but struck boldly downward through soil so hard that it was removed by 
the use of a sharp iron instrument and only with great difficulty. 

LEAF-HABITS IN THE GHARDAIA REGION. 

Observations of the leaf characters of the desert perennials, as shown in 
November, offer some points of interest, especially since there had been 
no rain for a year previous to the visit. As would be expected, the leaf- 
habit is various, ranging from scale-like or none to fair size. Several species 
appear to be evergreen, including Artemisia herba-alba, Capparis spinosa, 
Eckium humilis, Fagonia bruguieri, Gymnocarpon sp., Haloxylon articulatum, 
Helianthenmm sessiliflontm, Henophyton deserti, Herniaria Jruticosa, and 
Salsola. Certain plants probably, as Henophyton, are facultative ever- 
greens, retaining the leaves if the season is moist and dropping them if it 
is excessively dry; several of this genus were seen wdthout leaves, but with 
green stems. (See, also, figs. 39, 40, and 41.) 

Some idea of the variation in size of the leaves of a single species, as well 
as the average size of the leaves, will be had from the results of a few meas- 
urements. The leaves of Henophyton deserti range in length from 2 to 3.1 
cm., and in breadth from 0.2 to 0.5 cm. The average length of 12 leaves 
from a single branch 7 inches in length was found to be 2.82 cm. ; the average 
breadth was 0.35 cm. On another branch, 23 cm. long, were 35 mature 
leaves which averaged almost exactly the size of those just given. Since 
these leaves are rather ntmierous and of good size, it will appear at once 
that the species has a relatively large leaf-stu-face, even if the area can not 
be stated more definitely. (Fig. 30.) 

The evergreen shrub Capparis spinosa has the largest leaves of any plant 
native to the Ghardaia region, and probably of southern Algeria. Its leaves 
are bilateral and nearly round and are placed upright on the branches; a 
series of 29 leaves from one branch 33 cm. long varied from 2 to 3.2 cm. 
in length and slightly less in width, the average being, length 2.9 cm., 
breadth 2.2 cm. 

Euphorbia guyoniana has a deciduous leaf -habit. Its leaves are rather 
small but numerous. A shoot 22 cm. long bore 40 leaves varying in length 
from 1.5 to 2.1 cm. and in breadth from 1.2 to 2.0 mm., with the average 
length and average breadth 1.7 cm. and 1.6 mm. respectively. 

It is worth noting that the surface of the leaves, as shown by inspection, 
is, possibly, most often smooth, as, for example, in Capparis, Henophyton, 
and Haloxylon. Dense hairiness is an exception among the species seen, 
Lithospermum callosum being the only plant striking in this regard. 

GROWTH AND FLOWERING HABITS IN THE GHARDAIA REGION. 

Upon arriving at Ghardaia in November, it was surprising to find several 
species of perennials, under strictly desert conditions, putting on new 
growth, forming fresh leaves, or coming into flower. Especially was this 



50 BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 

unexpected in view of the fact that no rain had fallen in the region for 
twelve months. A study of the roots in relation to the depth to water 
showed also that most of the native plants, during the dry season, could 
not have penetrated to a depth anywhere near that of the water-table of the 
valley, and the water relations of the plants growing on the plain above the 
M'Zab Valley were even more severe. Further, most of the species do not 
possess water-storage faculty. It should be noted that the only apparent 
difference in the water relation between November and in early autumn, 
or summer, was that of raising the relative humidity of the air through the 
lower temperature. In a preceding section it has been stated that little 
or no evaporation took place at night in November at Ghardaia, and pos- 
sibly less in the daytime than v/ould have been supposed. The leading 
environmental changes were, of course, the lower daily temperature and 
the really cool nights. 

It is not uncommon in the Arizona desert for a species to form flowers 
or leaves, following a change in temperature, the moisture conditions being 
not otherwise changed, but, so far as I know, the temperature changes 
bringing about this result are alwaj^s from a cooler to a warmer condition 
and not the reverse. It would not be expected, consequently, that in the 
present instance a renewal of vegetative acti\dties would follow as a direct 
result of a lower temperature, although analogous changes are necessary 
before certain species, after rest, will start developmicnt. Whatever may 
be the immediate cause of the renev/al of acti\dty on the part of the plants 
at Ghardaia as noted, the following species were seen to liave formed new 
leaves: Henophyton deserti and Zilla macroptera; also the following fresh 
flowers with or without shoot growth : Fagonia hruguieri, Haloxylon articti- 
latum, Henophyton deserti, Ononis polyclada, and Zillikoferia resedifolia, and 
three other species not determined. 

GHARDAIA TO TOUGGOURT. 

From Ghardaia the route, consisting of camel trails onl}', pursued a 
course south of east to Ouargla, and from Ouargla a direction east of north 
to Touggourt, over 400 kilometers, Ouargla being about half-way. There 
are no villages between Ghardaia and Ouargla and none between this place 
and a point 20 kilometers south of Touggourt, so that in accounts of the 
vegetation or the topography, lacking convenient points around which to 
center descriptions, the device will be adopted of using distance estimations 
to or from the three chief towns. 

The trail followed the valley of the Oued M'Zab, or kept close to it, for 
63 to 73 kilometers before finally leaving it. It passed the sister towns of 
Ghardaia and crossed short intervals of plain, descending occasionally to 
the oued. The walls of the M'Zab Valley, 60 meters more or less at 
Ghardaia, become lower and less precipitous as one goes down the drain- 
age, until at length they become little more than rounded banks. The 



GHARDAIA TO TOUGGOURT. 5 1 

low, flat-topped mountains, which are a feature of the topography about 
Ghardaia, were soon left behind, and nothing similar was encountered 
until the vicinity of Ouargla was reached. Between Ghardaia and EI 
Ateuf are small dunes in the valley and sand is drifted along the base 
of the walls at various places. Near and immediately east of this town 
the sand is especially abundant and, being shifted by the winds, con- 
stitutes an ever-present menace to the small gardens belonging to the 
inhabitants of the place; in order to control its drifting, fences of palm 
leaves are made or the sand is removed when it becomes too abundant. 
Often the gardens are abandoned, leaving the palm fences to mark their sites 
after the sand has gone beyond. Where the air-currents are most powerful 
or most consistent, or the walls are broken down, the sand may be car- 
ried in small quantities onto the plain, where it constitutes a mulch, influ- 
encing in a striking manner the character of the vegetation (fig. 42). 

Finally leaving the valley of the M'Zab about 73 kilometers from Ghar- 
daia, the trails wound upwards through low rounded hills to the hamada. 
This is the northern edge of the region of the Gantara, 100 by 1 50 kilometers 
or more in extent, reaching from the valley of the M'Zab on the north to 
the region of the dunes to the south. It slopes towards the Oued Igharghar, 
or the drainage depression connected with this great oued. The Gantara 
has a few chotts and is crossed by three oueds in the southern portion. 
It is probably the most arid part of southern Algeria. About 60 kilo- 
meters of the plain were crossed and here it was gently rolling and stretched 
without a break to the horizon. The surface resembles that of the hamada 
at Ghardaia, that is, stones of various sizes, usually small, lie on its surface, 
but never forming a continuous cover, as in some portions of the Arizona 
desert. The soil is brown, of fine grain, and with little or no addition of 
sand. In the innumerable little hollows the soil is deeper than on the 
slight rounded ridges. Wind is apparently the most potent erosive agent. 

Two chotts were encountered between Ghardaia and Ouargla, one unim- 
portant, the other large and with many features of interest. The latter, 
the Chott Mellala, is about 10 by 15 kilometers in size. The trail descends 
from the plain, winding through a zone of rounded, cone-shaped hills or 
mamelons, to the floor of the chott, which lies about 60 meters lower than 
the general level of the plain. The chott was quite dry in November when 
we xnsited it, but at rare intervals water is said to flood the central portion. 
Toward the outer edges the floor is thrown into waves, where the heavy 
incrustation of salts is broken. In the center the salt crust forms an un- 
broken and level surface. Gypsum (calcium sulphate) is the predominant 
salt. On the eastern side a long and high ridge of sand rears its uneven 
summits. The height of this ridge was estimated to be 250 meters, and 
was said by JVIassart to be the largest seen by him in the Sahara. This 
dune we had seen lying on the eastern horizon for one or two days before 
reaching the chott. 



52 BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 

The relation of the Chott Mellala to the country to the north or the south 
was not seen, but between it and Ouargla there Hes a succession of smaller 
and more irregular chotts, which together form a fairly well-connected 
chain. These chotts are separated by low passes and flat-topped hills 
whose summits are on a level with the neighboring plain. Many of the 
hills are cone-shaped and in other topographic features the region shows 
the eroding action of wind. About 7 kilometers from Ouargla an opening 
in the mamelons gives a view of a plain extending on a lower level to the 
horizon. This is the reg, or fluvial desert. The Ouargla plain, or reg, is 
connected with the drainage of the great Oued Ighaghar and has a char- 
acter which in many ways is different from the Gantara, over which we 
had just passed. 

With the descent to the reg desert a more monotonous region is en- 
countered. In the vicinity of Ouargla and for some kilometers to the north 
the topography is quite flat and gives the impression of a flood-plain. To 
the east it stretches unbroken to the horizon, but to the west it is bounded 
by a fairly abrupt wall, the Gantara escarpment. At intervals of several 
kilometers low sand ridges cross the route over the plain, and on the second 
day somewhat higher ground was traversed and a sand ridge about 4 kilo- 
meters across was encountered. The country then becomes somewhat 
more broken and presents the appearance of being the remains of an ancient 
and more elevated plain. About 56 kilometers from Ouargla are the largest 
dunes crossed; where traversed, these were 10 kilometers from north to 
south and extended beyond our vision both to the east and the west. This 
is apparently the edge of extensive dune regions which lie mainly east of 
Touggourt and of the Oued Rirh. For possibly the last 30 kilometers of 
the joiuney to Touggourt there are dunes and chotts in alternation. 

A word should be said regarding the hydrography of the region whose 
surface featiu"es have been sketched above. Between the cities of Beni 
M'Zab and Ouargla two wells were passed, although a route could have 
been taken which could have included three wells. The wells are 125 meters 
or less in depth and are maintained by the government for the benefit of 
the caravans, as well as to provide water for the large number of goats 
and sheep pasttu-ed in the neighborhood. The situations of the wells are 
always in depressions, either along the Oued M'Zab or in similar although 
smaller drainage areas, and none are on the Gantara. At Ouargla and on 
the reg desert to the north of the town the water lies very close to the 
surface of the ground. It can be dipped with buckets and the roots 
of the palms reach to the water-table. The water from the shallow wells 
is strongly impregnated with salts. Before reaching Touggourt standing 
water was seen where the trail crossed certain chotts. Numerous artesian 
wells have been made by the government which penetrate the ground 
several hundred meters and give a large and continuous supply of sweet 
water. 



GHARDAIA TO OUARGLA — VEGETATION. 53 

GHARDAIA TO OUARGLA— VEGETATION. 

The plants seen during the first day's march from Ghardaia were such 
as have already been observed to be characteristic of the valley of the Oued 
M'Zab or of the neighboring hamada. The vegetation of the hamada, 
usually very sparse, was noticeably more abundant wherever the sand had 
been drifted over it from the dunes of the valley, even if the thickness of 
the sand was so slight as to be Httle more than a mulch. Here low grasses, 
much eaten, were the prevailing forms. On the dunes in the valley of the 
M'Zab, 20 kilometers from Ghardaia, the number of species and individuals 
is relatively large, the most abundant species being drinn {Aristida pun- 
gens), although D even a scoparia is also fairly numerous. Somewhat farther 
on the route, and in a sandy flat, besides these two species, there is much 
Ephedra alata. On the slopes leading from this flat and on the plain above, 
there is an almost piu-e stand of Rhantherium adpressum. 

Crossing relatively small portions of the plain, in place of always follow- 
ing the bends of the Oued M'Zab, about noon of the second day we reached 
the bordj Zolfana, in the valley of the Oued amidst low and narrow dunes, 
which are moving slowly across the flats. (Fig. 441.) No vegetation 
appears on the dunes, but on the fixed sand between them, or on the 
stationary dunes at the border of the flats, some plants are to be found. 
Among these the most abundant, but really not numerous, are Euphorbia 
guyoniana and retam (Retama retam) , which was often seen later along the 
line of march as well as in the \dcinity of Biskra. Retam superficially 
resembles Ephedra alata in having rudimentary leaves and green, reed-like 
branches ; it is carefully avoided by animals, although Genista saharce, a very 
similar plant, which grows in like situations between Ghardaia and Ouargla, 
is said by Massart (loc. cit.) to be eaten greedily by them. (Fig. 43.) 

A short distance beyond the bordj the bottoms suddenly widened, the 
dunes disappeared, and for the remainder of the day's march we passed 
through the richest vegetation we had seen since reaching the M'Zab region. 
(Figs. 45, 46, and 47.) Here the shrubs were of fair size and of sufficient 
abundance to give character to the landscape. About the 63 kilometers 
camp the leading species are Retama retam, Ephedra alata, and Haloxylon 
schmidtianitm. On the hamada adjoining the flat are several species, in- 
cluding Aristida ciliata, Artemisia herha-alha, Farsetia cegyptiaca, Farsetia 
linearis, Gymnocarpon fruticosum, Helianthemum eremophilum, Henophyton 
deserti, Marruhium deserti, Salsola vermiculata, Teiicriiim poUum, Thymelcca 
microphylla, and Zollikoferia mucronata. On the hamada just adjoining the 
place of our camp, however, there appeared to be Haloxylon schmidtianitm, 
to the exclusion of other species. 

After crossing the bottoms of the oued the trail climbed up to the hamada 
and we did not see the M'Zab Valley afterward. The vegetation of the 
hamada soon becomes very sparse and as far as the eye can reach the ap- 
pearance is that of entire bareness. But, as was found to be the case near 



54 BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 

Ghardaia, close examination revealed the presence of many living perennials 
as well as the remains of the previous annual flora . This plain, the Gantara, 
of wide extent, is the most arid region seen in southern Algeria. Massart 
estimates that there is an average precipitation of 15 cm. on the desert, 
but, from data previously cited, it would appear that this amount is rarely 
attained; indeed, several months, or even two or more years, may pass 
without any rainfall whatev^er. When one searches the hollows he finds a 
few small perennials; plants are almost wholly absent on the low ridges. 
But in some areas on the plain, where superficial examination does not 
show any plants, a surprising number were found. For example, on the 
level hamada, 96 kilometers from Ghardaia, on an area 16 meters square, 
389 Hvnng plants were found, but only 24 were so large as to be seen from 
a distance; all were either eaten badly or trampled to the ground, so that 
it could not be learned what the flora of the area inight have been had no 
animals interfered with its full development. 

After leaving the 96 kilometer station the perennials were seen to dimin- 
ish rapidly in numbers and to decrease in size, until the ridges of the low 
undulations were absolutely without plants, and there were but few in the 
hollows. There was no apparent change in the character of the hamada 
or in that of the soil. This sterile condition persisted for 26 kilometers, 
when vegetation similar in character to that previously seen was again 
encountered. The zone of better vegetation lasted for 3 kilometers, when 
the country became barren once more, which condition lasted for 10 kilo- 
meters. The presence of barren belts on the Gantara, where the plants at 
the best are insignificant in size as well as number and without change in 
topography or soil, points to an especially arid belt. This conclusion is 
further strengthened by the observation that the plants found were rela- 
tively of very small size.* 

The flora was also sparse upon the route followed by Massart across the 
Gantara, which was apparently somewhat farther to the north than the one 
now being described. He mentions having found Argyrolohium imiflorum, 
Astericus graveolens, Fagonia microphylla, Deverra chlorantha, Fagonia gluti- 
nosa , Halogeton alopecuroides, Helianthemum sp . , and Herniaria fruticosa. He 
says that Deverra is one of the rare glabrous forms on the hamada. It is 
said to have the odor of parsley, and the Arabs have a beUef that camels 
which eat it become Wind, but Massart's camels were not injured by eating 
the pla,nt. 

As we drew near the Chott Mellala, on the eastern edge of the barren 
zone mentioned in the preceding paragraph, we suddenly encountered a 
belt of Ephedra alenda, stretching to the north and to the south as far as 

* In the case of annuals the differences in development of the shoot between plants 
well watered and those with only a meager supply are very striking. In one instance 
in the Tucson region specimens of Parietaria debilis growing in extreme conditions, one 
moist and the other arid, varied in length between 39 cm. and 8 mm., or a difference 
with a ratio of 49 to i. (Root Habits of Desert Plants, loc. cit.) 



GHARDAIA TO OUARGLA — VEGETATION. 55 

could be seen (fig. 49). On one side was the barren zone, on the other the 
immense plantation. Upon examination it was found that the Ephedra 
was the only species of perennial. It had sev^eral points of interest, but 
the short time at our disposal precluded more than a superficial examina- 
tion. Usually keen about the desert species, it is curious to note that the 
Arabs appear not to recognize this, called by them "alenda," as being re- 
lated to the larger species of Ephedra with which they are well acquainted. 
It is a small species, growing from 30 to 40 cm. high. It does not occur 
singly, but has the habit of growing in groups of a half dozen or more. 
Between the Ephedra colonies were only the dried remains of the annual 
flora of the last rainy season. An examination of the root-system of the 
species showed that, like other species of the genus, it has a well-developed 
tap-root (fig. 50). 

Alenda, however, has a root-habit which, although not peculiar to it, is 
at least very striking and of great importance to its survival. From the 
root-crown a stolon arises which extends away from the parent for a distance 
of about a meter. From this stolon there arise shoots which develop into 
daughter plants. Through this method of reproduction the small colonies 
of the species are formed and possibly the species mainly multiplied. From 
the stolons small roots arise, giving aid to the mother root in providing the 
offspring with moisture. This habit is very like that of Kceherlinia spinosa 
of the Arizona desert, which has a similar type of root-system and which 
reproduces vegetatively in a similar manner. Alenda continued to be the 
dominant species until near the edge of the big chott (Mellala) , a few kilo- 
meters east of where it was first seen. 

Practically no plants were seen when descending through the eroded 
portions of the hamada to the floor of the chott (fig. 52), but on reaching 
the bottom of the great chott a surprisingly large number was observed, 
including Anabasis artictdata, Aristida pungens, Ephedra alaia, Limonias- 
trum guyonianum, Retama retam, and Traganum nudaium (fig. 51). In the 
wide central part of the chott, where the salts are perhaps most dense, 
there are no plants; but on the eastern side are Euphorbia guyoniana, 
Anabasis artictdata, and Zygophyllum sp. These small species were grow- 
ing far apart and were badly injured, either by being trodden under foot 
or by being eaten by the passing animals. To the south of where we 
crossed the chott and also to the north the sand mountains arise. After 
leaving Chott Mellala we ascended gradually to go over a low pass sepa- 
rating it from a small chott to the east. Here we obtained a backward 
view of the sand mountains, low as seen from the pass, with sharp, wind- 
made ridges, and bearing a few specimens of Aristida pungens. Descend- 
ing somewhat, another but smaller chott was crossed. Between the latter 
chott and the Ouargla plain the plants were very few and confined to the 
slopes and the higher ground, avoiding almost wholly the depressions. Of 
those recognized, Tragonum nudatiim was the most abundant. This is the 



56 BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 

"vamran" of the Arabs and is an inconspicuous shrub frequently seen 
later on the way to Touggourt. 

OUARGLA TO TOUGGOURT— VEGETATION. 

Ouargla is an ancient, rambling town, somewhat in decay, set in the 
midst of extensive palm gardens. There are said to be 500,000 date palms 
at the oasis. It was founded in the tenth century by the M'Zabites and 
later taken possession of by the Arabs. The town is peculiar in its situa- 
tion and its gardens, lying, as before described, in the flood-plain of an 
ancient river. The plants cultivated in the town as ornamentals are fewer 
than at Ghardaia, but of the same kinds, and (besides dates) the gardens 
contain fewer fruits and apparently fewer kinds of vegetables. Between 
the gardens one finds Tamarix in some abundance. 

Leaving Ouargla by the western gate and turning north, we soon passed 
through the crooked streets and reached the reg desert to the north. There 
is little vegetation near Ouargla, but on some low dunes extending over the 
reg we found Aristida pungens and Phargmites sp., growing in a hollow. 
On the flood-plain there were a large number of individuals and probably 
a large number of species. Among the most conspicuous of the shrubs were 
Retania reiam and Ltmoniastrum giiyonianum, the "zaita" of the Arabs. 
(See figs. 56 and 57.) Zaita is a handsome shrub with cylindrical leaves often 
covered with a fairly heavy salt incrustation. So abundant is the exuda- 
tion that in localities where the species is especially abundant, as at our 
camp 32 kilometers south of Touggourt, the plants have the appearance of 
being covered with snow. Although, like many other species between Toug- 
gourt and Ouargla, zaita can Uve where there are salts in excess, it appears 
not to be an extreme type of halophyte and does not occur where the salts 
are most dense. It was seen both on the dunes and on the low lands. 
Other common halophytes are "souid" (Salsola tetragona), "belbel" (Awa- 
basis sp.), and Halocnemon strobilaceum, which appears especially resistant. 
(See figs. 59, 60, 61, and 62.) 

Other forms appear on the higher ground and on the plain about 50 kilo- 
meters from Ouargla, where Ephedra alata especially is common. There 
are no dunes on the plain, but some sand swept across it from the fluvial 
desert to the west passes eastward and augments the dunes farther east. 
The larger specimens of Ephedra are rather effective sand-binders and bring 
about the formation of diminutive dunes. The effect on the growth of the 
species by the piling sand is peculiar. As the sand acctmiulates it covers 
the lower branches of the shoot; these are stimulated to unusual growth 
and new branches may spring from them. Thus the effect is similar to 
that habitually occurring in E. alenda, but in E. alata the habit is not a 
fixed one. As an instance of the length which such submerged branches 
may attain, it may be mentioned that one, 2 to 3 cm. in diameter, was over 
4 meters long. 



OUARGLA TO TOUGGOURT — VEGETATION. 



57 



About 75 kilometers from Ouargia, and on a plain similar to that just 
referred to, "dhamran" (Traganum nudatum) was the most common 
species, but was by no means abundant. The census of an area i6 by i6 
meters, taken in a locality where dhamran was dominant, resulted in find- 
ing 31 living and a few dead plants, probably all Traganum. It is to be 
understood that the vegetation of the reg desert not far distant is much 
richer, not only in species but especially in individuals, and also that the 
plants are much larger. 

From 56 kilometers to about 71 kilometers from Ouargia the route lay 
over more or less continuous dunes, where the leading species seen were 
Aristida sp., Ephedra sp., Euphorbia guyoniana, Limoniastrum guyonianum, 
and Traganum nudatum. 

In or about the edges of the chotts, which are the leading topographical 
features of the region immediately south of Touggourt, the most common 
species are Haloxylon sp., Salsola tetragona, Limoniastrum guyonianum, and 
Arahis aphyla. Besides these forms, about 28 kilometers south of Toug- 
gourt fine specimens of Halocnemon strobilaceum were seen growing in an 
extremely salty situation, to the total exclusion of other species. Tamarix 
also is to be found in and about salt spots near Touggourt. (See fig. 64.) 

Both Massart and Doumet-Adanson (Bull. Soc. Bot. France, 39, 1892) 
have discussed the flora of the Touggourt-Ouargla region. The following 
exhaustive list is given by the latter author as having been collected between 
the two desert towns: 



Henophyton deserti. 
Matthiola livida. 
Malcolmia aegyptica var. 

linearis. 
Maricandia cinerea. 
Sisymbrium pendulum. 
Savignya longistyla. 
Reseda stricta. 
R. arabica. 

Helianthemum sessiliflorum. 
H. ellipticum. 
Randonia africana. 
Frankenia pulverulenta. 
Silene nicoeensis. 
Monsonia nivea. 
Erodium glaucophylum. 
Fagonia glutinosa. 
F. frutescens. 
Polycarpaea fragilis. 
Gymnocarpus decandrus, 
Retama retam. 
Genista saharae. 
Astragalus gumbo. 
Anthyllis henoniana. 
Neurada procumbens. 



Ammodaucus leucotrichus. 
Mesembryanthemum sp. 
Deverra chlorantha. 
Nolletia chrysocomoides. 
Senecio coronopifolius. 
Anthemis monilicostata. 
Tanacetum cinereum. 
Ifloga fontanesii. 
Centaurea purpuracea. 
Amberboa omphalodes. 
Rhantherium adpressum. 
Atractylis flava. 
A. prolifera. 
A. microcephala. 
Tourneuxia variifolia. 
Catananche arenaria. 
Spitzelia saharce. 
Zollikoferia chondrilloides. 
Z. squamosa. 
Sorzonera nudulata. 
Echium humile. 
Echiochilon fruticosum. 
Arnebia decumbens. 
Statice pruinosa. 
Limoniastrum guyonianum. 



Plantago ciliata. 
P. psyllium. 
Scrophularia saharas. 
Linaria fruticosa. 
Euphorbia guyoniana. 
Atriplex dimorphostegius. 
Caroxylon tetragonum. 
Echinopsilon muricatus. 
Calligonum comosum. 
Haloxylon articulatum. 
Anabasis articulata. 
Cornulacea monocantha. 
Thymelea hirsuta. 
Th. microphylla. 
Aristida flaccosa. 
A. pungens. 

Cyperus conglomeratus. 
Ephedra fragiHs. 
Erythrostictus punctatus. 
Scilla sp. 

Dipcadi serotinum. 
Asphodelus pendulinus. 
Ruppia maritimus. 
Chara foetida. 



58 BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 

TOUGGOURT TO BISKRA— PHYSICAL FEATURES AND VEGETATION. 

From Oiiargla to Touggourt we have found that the country gradually 
descends, the former place being 124 meters and the latter 77 meters above 
the level of the sea. From Touggourt, also, for a distance of about 120 
kilometers, the descent along the route continues until at the Chott 
Merouan a level of 6 meters is attained. The lowest places in every case 
are of course the chotts and the connecting oueds. The most important 
chott of this series is Melrirh, 11 meters or more below sea-level. This 
drainage system is the northern culmination of the vast one of which the 
Oued Igharghar is the most important part. In an earlier age water came 
north in the oued from the highlands of central Sahara and poured into 
the Chott Melrirh, having passed successively through the lesser chotts 
farther south. At that time, also, the Chott Melrirh probably was con- 
nected with the Gulf of Gabes. 

From Touggourt to Chott Merouan, the lowest portion of the route to 
Biskra, the topography is that of a region of chotts ; that is, there are salt 
spots surrounded on every side by higher ground, which in many cases is 
of sand. From Chott Merouan the route passes over a higher desert of a 
different character, which in part bears a remote resemblance to the Gantara 
and in part to the Ouargla plain. It is a vast plain, with little topographical 
diversity, which rises to meet the Atlas Mountains to the west and north. 
In the eastern portion it is somewhat rolling, stones are strewn plentifully 
on its surface (hamada), and there has been considerable erosion, so that 
gullies are formed. In the portion nearer Biskra the surface is more level, 
the soil is fine (reg), and there has been comparatively little erosion. 

The soil of the chott region is largely of sand; on the hamada there is 
much clay, while on the reg it is fine and easily blown by the wind, and this 
in spite of the fact that the most vegetation seen in the Sahara was in this 
region. A slight breeze picks up the dust and carries it long distances in 
dark clouds. It fills the throat, nose, and eyes of the traveler and makes 
crossing the reg exceedingly disagreeable. 

The plant life as seen along the portion of the route through the chott 
region consists almost wholly of halophytes, as would be expected, in addi- 
tion to which, where for short distances the hamada or dunes were crossed, 
there were forms characteristic of such areas. The Tamarix is especially 
common in the region and Limoniastrum guyonianum is also often met. 

The date gardens of the Oued Rirh are justly famous. One passes num- 
berless plantations where the date is cultivated, and in the neighborhood 
of each group of gardens one sees squalid Arab villages. Over 19,000 tons 
of dates are said to be carried each year by camel from the Oued Rirh to 
Biskra, whence they go to the markets of the world. One day we passed 
700 camels laden with dates going to Biskra. 

As soon as the chott region is left and the higher ground is reached a dif- 
ferent as well as a richer flora is encountered. Here diversity of topography 
favors diversity of plant life. On the reg near Biskra vegetation is especially 



THE BISKRA REGION. 59 

abundant. Here, in fact, one passes through large thickets of Tamarix and 
other species, and sees that the desert is much less intense than that in the 
south, especially in the region of the M'Zab, where in many respects the 
topography is similar. The kinds of plants also, as the hst below will 
indicate, are different in the main from those farther to the south. Where 
the surface is most rolling we find Tamarix sp. on the heights, Zizyphns lotus 
in the hollows, and the following grasses: Stipa tortilis, Hordeum mariti- 
mum, and Phalaris minor. A salsolaceous shrub {Arthrocnemon m,acrosta- 
chynm) may be found in washes, Nitraria and Limoniastnim gtiyonianum 
on sandy places, and Odontospermum pygmceum and Anastatica hierochun- 
tica occur between rocks. On clay flats one finds Halocnemon strobilaceum 
and Sucsda vermiculaia, indicating the presence of salts. 

The preceding notes are in part from Massart. The following species 
are given by Doumet-Adanson as having been collected by him between 
Biskra and Touggourt : 

Savignya longistyla. Nitraria tridentata. Nonnaea micrantha. 

Eremobium lineare. Astragalus gyzensis. Lithospermum callosum. 

Lonchophora capiomontana. Ononis serrata. Heliotropium undulatum. 

Monsonia nivea. Ammodaucus leucotrichus. Plantago ciliata. 

Erodium pulverulentum. Cyrtolepis alexandrina. P. albans. 

Fagonia sinaica. Anacyclus clavatus. Limoniastrumguyonianum. 

Haplophyllum tuberculatum. Pyrethrum fuscatura. Statice pruinosa. 

Loefflingia hispanica. NoUetia chrysocomoides. Echinopsilon muricatus. 

Paronychia nivea. Tanacetum cinereum. Traganum nudatum. 

P. cossoniana. Ifloga fontanesi. Ephedra alata. 

Herniaria fruticosa. Artemisia herba-alba. Cutandia memphitica. 

Zygophyllum album. Anvillaea radiata. Erythrostictus punctatus. 

Z. cornutum. Atractylis flava. Asparagus albus. 

Peganum harmala. A. prolifera. Aristida pungens. 

% 

THE BISKRA REGION. 

TOPOGRAPHY.* 

Biskra lies immediately south of the Atlas Mountains, in the Depart- 
ment of Constantine, 220 kilom^eters from the Mediterranean and about 
400 kilometers from Ouargla. To the northeast of the oasis lie the Aur^s 
and to the west the beginning of the Saharan Atlas, which run south of 
west across Algeria into Morocco. Just north of the place are small hills 
and low, jagged mountains — detached spurs from the main ranges. These 
are the Djebel Bou Rhezal, running nearly northeast and southwest. The 
highest of them, directly west of Biskra and about 8 kilometers distant, 
has an altitude of 463 meters. The Bou Rhezal Mountains have a precipi- 
tous southern face, but fall away more gradually to the north, where the 
slope joins a wide and undulating plain. The latter extends to the base 
of the main Atlas ranges. Southwest of the oasis, and about 2 kilometers 
distant, a range of rocky hills extends for a distance of about 6 kilometers, 
or until they join the mountain range of the Saharan Atlas. These hills 

* The vegetation in the vicinity of Biskra is so well known that a sketch will suflBce 
as a basis of comparison with the flora and conditions of plant life farther south. 

5 



60 BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 

are called Ed Delouatt. To the south of Biskra, as has already been 
stated, there extends a vast plain, the reg, which dips gently to the south 
and drains into the Chott Melrirh, 50 kilometers or more distant. The 
situation of Biskra relative to the mountains on the one side and the desert 
on the other, together with its altitude, governs the climate of the place. 
Except Laghouat no vicinity in the desert proper was seen with so great 
an amount of precipitation (about 200 mm.) as Biskra, which is indicated 
by the relatively rich flora. One who has seen only Biskra can not draw 
conclusions regarding the vegetation or the conditions of plant life of those 
portions of the Sahara that lie farther to the south, where much more 
intense conditions of aridity obtain. 

The soils of the vicinity of Biskra are various. That of the low hills 
between the town and the Djebel Bou Rhezal is only a few centimeters in 
thickness, but in the washes from the hills it is a meter or more. Here the 
soil is a sandy loam with an admixture of sm.all stones and pebbles. On 
the fiat ground to the north and to the south of these hills it is of a finer 
texture, approaching the adobe of the southwestern United States. On the 
reg to the south of the oasis the soil is also fine, and in some places, if not 
underlying the plain as a whole, there are strata of gravel at varying depths 
beneath the surface. This soil in places carries considerable salts. It dries 
to a powder during the long dry seasons and is easily blown by the winds. 
Owing to outcropping rock, the south face of the Bou Rhezal Mountains 
has but scant soil, but that of the northern side resembles the soil of the 
low hills to the south, which has already been characterized. Near the 
town are dunes of good size. Especially to the southwest the sand banks 
against Ed Delouatt hills is in large amount. In the opposite direction, 
but farther from the oasis, the dunes are fairly extensive. 

The Oued Biskra is of great importance to the oasis, since it carries water 
for several weeks of the year and furnishes water for irrigation. Its channel 
lies about 3 meters, or possibly more, below the general level of the oasis, 
and possibly in earlier times may not have been so well defined as at present, 
spreading its waters over its flood-plain during high water. The oued is 
made up of several tributary oueds which cross the plain north of Djebel 
Bou Rhezal, unite where there is a pass in these mountains, and finally 
debouch on the reg to the south of the town, where the channel becomes 
continually less well defined. Another oued takes its origin in the Bou 
Rhezal l^.Iountains in several independent branches which unite at a pass 
in Ed Delouatt hills and extend for a distance of 1 5 kilometers or more into 
the reg. One of the feeders of this oued is from hot springs, Hamman es 
Salahine, about 8 kilometers northwest of Biskra. 

PLANT HABITATS OF THE BISKRA REGION. 

From the preceding sketch of the leading topographical conditions of 
the vicinity of Biskra it will be seen that the plant habitats are more diverse 
than at any other place visited. For the present purpose the habitats may 



THE BISKRA REGION. 6l 

be distinguished as follows: The alluvial desert (reg), which lies on every 
side of the oasis save the north ; low hills adjoining the oasis on the north ; 
Ed Delouatt hills, southwest; the oueds and their flood-plains; the Dj. Bou 
Rhezal ; the hamada ( ?) lying both to the north and to the south of the latter. 

VEGETATION OF THE BISKRA REGION. 

A glance over the list of plants which grow naturally in the vicinity of 
Biskra* shows that many are the same as occur farther south, with many 
unlike these, having affinities outside of the desert proper; also, the number 
of plants as well as species is greater at Biskra than farther south. This 
would be expected from the greater rainfall and more diverse topography. 

The flora of the Biskra oasis, according to the authors referred to above, 
consists of 175 or more species. Of cultivated plants there are 25 or more 
species, the most conspicuous being the date. The other species are mostly 
the same as have already been noted at other Algerian oases, except that 
both the peach and the apricot are wanting at Biskra, although cultivated 
at Laghouat, Ghardaia, etc. On the outskirts of the town the fairly ex- 
tensive flood-plain is given over mainly to the cultivation of grain, barley 
predominating. 

The hills and mountains, and the bajada at their base, as well as certain 
oueds with water relations, exposure, and soils different from those of the 
oasis, have also a very different flora, which, for the most part, is desertic 
in character. For purposes of comparison, some of the leading character- 
istics of the plants growing in a half-dozen localities will be given. 

As stated above, to the southwest of Biskra there runs a range of hills, 
Ed Delouatt, to the south and the north of which may be found interest- 
ing plants and plant conditions. On the south side the slope (bajada) 
descends gradually to the great reg, and near the base of the range, in the 
vicinity of the place where tradition says a Roman town formerly existed, 
there is a wide, sandy plain, reaching from the Oued Melah, which pierces 
Ed Delouatt hills, nearly or quite to the western extension of the oasis. 
There are no large dunes here, but sand billows about a meter in height 
and sand hillocks diminutive in size. Between these the plain is fairly 
level. Over this whole tract there seemed to be only one species (Euphorbia 
guyoniana), but this was fairly abundant. (Fig. 65.) As at Ghardaia and 
elsewhere, this species grows in small colonies because of its suckering habit, 
and acts to a small degree as a sand-binder, each group being situated on a 
sandy hillock. It will be remembered that tliis species at Ghardaia, as well 
as at a certain bordj east of that place, had roots which were somewhat fleshy 
as w^ell as roots which were fibrous, on one and the same plant. I was inter- 
ested to learn whether similar conditions should obtain at Biskra, since it 
had been learned, in the case of two species of Opuntia in the Tucson region, 

* Liste des plantes observ^es aux environs de Biskra et dans I'Aur^s, Trabut et al., 
Alger, 1892. 



62 BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 

that a different habit followed certain differences in habitat. Several speci- 
mens of Euphorbia were removed with care from the soil and in no case was 
it found that the roots were fleshy, but in every instance they were entirely 
fibrous. It is supposed that the reason for the variation in behavior may 
possibly be traced to differences in the v/ater relation, as was found to be 
the case of the variation in cactus roots cited, but no experiments have 
been made on Euphorbia to prove this.* 

There is a variety of habitats on the opposite (north) side of the hills, 
ranging from the large dune (which reaches the summit to the west of the 
pass through which the oued passes and which must be loo to 150 meters 
above the oued) to the flood-plain, with water very near the surface, during 
rainy season at least. There are rocky slopes, also, and sandy slopes apart 
from the dunes referred to, as well as a fine clay with sand admixture on 
the flood-plain. In all of these habitats, except the large dune, the vege- 
tation is actually or relatively abundant. (See fig. 67.) Among the rocks are 
small shrubs or half-shrubs, and also on the plain below. Here one may find, 
among other species, Echiochilon Jruticosum, Helianthemum sp., Atractylis 
serratuloides, Gymnocarpos Jruticosum, Thymelcea microphylla, Nitraria tri- 
dentata, and AcanthylUs tragacanthoides. On the sandy slope was growing a 
very numerous population of liliaceous forms, mainly, perhaps wholly, 
Asphodelus fistulosus (fig. 72). 

It has been noted that the oued which pierces Ed Delouatt is made up 
of the confluence of all of the small oueds lying between the Bou Rhezal 
Mountains to the north of Biskra and the hills lying directly north as well 
as those (Ed Delouatt) to the southwest. The united oueds reach the base 
of the hills nearly i kilometer east of the pass, and turning abruptly follow 
the base the remainder of the distance. At the place where the oued touches 
the range the soil is moist nearly to the surface of the plain (reg) and for 
several meters back from the oued. Here, then, the water relations of the 
plants are such as to favor, probably most of the year, the growth of meso- 
phytes ( ?) or even of hydrophytes, but for some reason there is not much 
vegetation there; whether large species have been removed as for fuel, have 
been destroyed by animals, or never existed, was not learned. The most 
interesting plant found was the well-known parasite Phelypcea violacea, 
which grows, according to Mobius, on a salsolaceous host.f Only a few 

* Briefly the case is as follows (see The root systems of desert plants, loc. cit.) : Opuntia 
arbuscula growing near Tucson develops fleshy roots, but what is probably the same 
species growing about 100 miles distant has fibrous roots. Also, seedling opuntias have 
fleshy roots. Opuntia vivipara, which occurs naturally in the bottom of an arroyo 
(oued), may or may not have fleshy roots. By preliminary series of experiments it was 
learned that all opuntias tested which had an abundant water-supply developed fleshy 
roots, and it is assumed from this that the differences in this character as observed in 
nature had also such a physiological basis. 

t Eine botanische Exkursion nach Algier and Tunis, Bericht der Senckenbergischen 
Naturforschenden Gesellschaft in Frankfort a. M., p. 76, 1910. 



THE BISKRA REGION. 63 

specimens were seen at the time of the second visit to Biskra, in March, 
and they were just appearing above the ground. (See figs. 69, 70, and 71.) 
When removed from the soil the longest specimen was found to have 
penetrated over 59 cm.; it was 6.5 cm. in diameter at a point 50 cm. from 
the tip. The plants were exceedingly heavy, being gorged with sap, and 
appeared to be able to absorb moisture from the wet soil through the white 
and dehcate epidermis of the entire portion submerged. If this is the 
case the parasitical relation is of especial interest, as the species is wholly 
dependent on its host for organized foods, but not for water — a condition 
opposite that found in such semi-parasites as the mistletoes, which obtain 
water and unorganized foods in solution from the host, but which, save 
for the fact of attachment, are otherwise independent of it. 

To the northeast of Ed Delouatt hills and north of Biskra, but immedi- 
ately adjoining the town, is an irregular group of low, rounded hills, mostly 
very arid, which support a scant vegetation of typical desert plants. These 
hills, without a name, are eroded to a degree and have shallow washes lead- 
ing from them in every direction. The soil appears to be thin, except in 
the washes, where it has accumulated to the depth of a meter or more. 
On the rounded summits it is rather fine, but in the washes there is much 
gravel and larger stones. Here one finds the greatest range in exposure, 
and probably also an accompanying difference in the temperature of the 
air and soil. 

In considering the vegetation of the hills it must be remembered that no 
plants suitable for forage or large enough for fuel would be left untouched, 
as the biotic factor is quite as much in evidence in modifying the Bislcra 
flora as that of the other regions visited. As the plants are at present, 
however, and for whatever definitive causes, there is a considerable varia- 
tion in numbers and apparently also in kinds. An examination of different 
parts of the hills by which various exposures as well as other conditions 
are seen bears out the hypothesis. On the southern slopes, particularly the 
upper portions, the plant covering is especially poor. The population of an 
area 16 by 16 meters in the upper south slope included 134 perennials 
and numerous annuals. Of the species, Haloxylon scoparium was the most 
numerous; there were also Dczniia cordata, Thymelcea microphylla, and 
Fagonia sinaica (figs. 78 and 80). All of these species were small, so that 
from superficial examination the area appeared fairly barren (fig. 73). 

When one crosses the hills to the north, so that northern and north- 
western exposures are seen, a striking difference is immediately apparent. 
The northern slopes are much richer in perennials than the opposite facing. 
The population of an area of the size before taken shows this observation 
to be correct. On a square 16 by 16 meters, with north exposure, 536 living 
perennials and numerous annuals were found, with Haloxylon scoparium 
again the dominant species. The species second in number was Ferula 
visciritensis, which is to be found chiefly on the north exposure (figs. 74, 



64 BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 

75, and 77). There were also a few specimens of Acanthyllis mtmidica, and 
many annuals, which, unlike those on the south facing, were not in flower. 

On the lower slopes, in the small and open gulches and the lower por- 
tions of the washes and their flood-plains, the plants were most numerous 
and include a variety of forms, with Peganum harmala the most conspicu- 
ous and most numerous. 

The roots of several species growing on the hills were studied with the 
following as perhaps the leading results: The root-system of Haloxylon 
scoparium, as has already been seen to be the case with an alHed species 
in the country of the M'Zab, may be said to be a modification of the gen- 
eralized type. One specimen, partly exposed by erosion in a wash, had a 
tap-root over 1 13 cm. in length (fig. 76) . As this root was 4 mm. in diameter 
where left, and was 8 mm. in diameter at the crown, it may have penetrated 
much beyond the point where it was left, provided the soil conditions con- 
tinued favorable. The main root gave off two large laterals, of which one 
left the parent root 8 cm. and the other 18 cm. beneath the surface of the 
ground, but there were also numerous filamentous roots about 2 cm. in 
length, which were borne in tufts. (See fig. 79.) These resembled the 
deciduous rootlets found on many perennials in the Tucson region and 
doubtless function quite as they, namely, they are organized at the begin- 
ning of the rainy season, operate to increase the water-absorbing area of 
the plant quickly and greatly, and die as soon as unbearably arid condi- 
tions set in. 

In the same wash, where the soil was deep with an admixture of small 
stones and pebbles, the roots of other species were also examined. One of 
these was Peganum harmala, whose roots v/ere examined at Ghardaia. The 
root-systems of the plant in the two regions were similar in being gener- 
alized. A main root was found extending downward over 61 cm. and 
it gave off three good-sized laterals, arising from 15 to 27 cm. beneath 
the surface. The uppermost lateral took a horizontal course. Figure 82 
gives a fairly good idea of the general character of the root-system of the 
species. 

There were many specimens of Plantago albicans growing in the same 
habitat as Haloxylon and Peganum. Its root-system was also studied with 
the following results : The tap-root is strongly developed. In one instance 
the slender main root was found to go straight down over 7 1 cm. Numer- 
ous laterals v/ere borne between 8 and 20 cm. beneath the surface of the 
ground. The species has an interesting habit of propagating vegetatively 
by means of fleshy stolons. An examination of the stolons showed them 
to be of very unequal age, some having been lately formed, while others 
had been organized in previous years and were no longer living. Many 
specimens were examined to learn the probable service of the fleshiness of 
its stolons, and the conclusion was that this factor probably enables the 
species to pass over periods of excessive drought. 



THE BISKRA REGION. 65 

Running across country are the Bou Rhezal Mountains, of which the 
north and south faces were examined in one or two places, on each side 
somewhat in detail. The south face is precipitous and has Httle vegetation, 
but there are many plants on the opposite face, especially near the base, 
where the soil conditions are relatively favorable (fig. 84). Among the 
perennials were found a few specimens of Rhus oxyacantha and Zizyphus 
lotus, which, although dwarfed, were the largest plants seen away from the 
oasis, being about 1.5 meters high. In another gulch were found the follow- 
ing species: Acanthyllis tragacanihotdes, Dcsynia cordata, Ferula vesciritensis, 
Haloxylon scoparium, and other plants unknown. Toward the upper por- 
tions of the gulches Haloxylon was seen to be especially abundant, but in 
the bed of the washes and on their flood-plains Peganum grows in large 
numbers (fig. ^2))- I^ the most favorable places on the northern slope in 
March the aimuals were the most abundant observed in the vicinity of 
Biskra, although even there they failed to completely conceal the ground. 
Where the situation was less favorable as regards soil and water conditions 
(for example, on the side of the gulches, on the summit of ridges, and the 
like) there were almost no annuals and those present were relatively small. 

In this brief account of some of the most striking features of the Biskra 
flora it should be noted that several habitats are omitted as not being 
pertinent to the points in view. Especially, nothing has been said regard- 
ing the flora of the salt flats along the Oued el Hamman or that of the 
dunes, since the influences here are largely edaphic, while the present in- 
terest lies mainly in the relation between plants and climate ; and the flora 
of the oasis has been largely neglected for similar reasons. 

Not only is there in certain regards a larger number of plants in the 
Biskra region than had been previously seen in southern Algeria, but there 
are certain types, mostly new, which point to more favorable conditions 
of plant life. These are such forms as have a water-storage habit, like 
Asphodelus, Ferula, Planiago, and Phelypcea, which, although not wholly 
absent farther south, appear to be much more numerous near Biskra. The 
presence of bulbous plants is well known as being one of the floral charac- 
teristics of the High Plateau, and it is also known that similar forms are 
not to be found where the arid conditions are the most severe, which prob- 
ably accounts for the facts noted. It may be pointed out also that plants 
at Biskra exhibit exposure preference where soil conditions appear to be 
parallel. This condition is not so marked farther in the desert as at Ghar- 
daia, for example, where, provided there is sufficient depth of soil, appar- 
ently any species may be found on any exposure. In other words, exposure 
preference implies a certain amount of water as well as sufficient soil. 

So far as shown by observations of the root-systems carried out on similar 
species growing in the Biskra region and at Ghardaia, the essential root 
characters of plants growing in the two regions are the same. The single 
exception to this so far noted is that of the roots of Euphorbia guyoniana, 



66 BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 

which, contrary to the expectation, are apparently wholly fibrous at Bis- 
kra, although they are in part fleshy farther south, where the soil conditions 
are surely more arid. At Biskra, also, the only plant observed with typi- 
cal generalized root-systems (Peganum) does not grow where the soil is 
shallowest, but where it is relatively deep. So far as seen, also, plants 
growing where the soil is shallow have either a generalized root-system 
or a root-system approaching this type, even if the branching is only 
relatively deep. 

GENERAL SUMMARY AND CONCLUSIONS. 

THE ENVIRONMENTAL CONDITIONS OF PLANTS IN ARID REGIONS. 

The environmental conditions encountered by plants in the arid regions 
are widely different from those of moister regions. Precipitation is not 
only slight, but it shows an enormous range in variation from year to year; 
the rate of evaporation is high; the temperature of the air and soil varies 
widely both during the day and with the seasons; the light is of great 
intensity, and the soil is low in humus content and may contain an excess 
of salts. These, the most striking physical factors of deserts, are present 
in different combinations with resultant differences among deserts, and an 
arid region may be so large as to include such variation within its borders. 
Also, a desert may be so far from the ocean, or it may include such 
diversity of topography, as to show great variation in biological features 
as well as in its surface phenomena. 

In the flora of any arid region, the mutual relations of the constituents of 
the flora and its general and detailed relation to the physical environment 
are quite different in the main from these features in the flora of the more 
humid regions. Thus, the leading relation is the relation to water, and on 
the response of the plants to this relation much of the phenomena associ- 
ated w4th plant life in the desert directly depends. For example, in the 
extreme deserts it is probable that the elements of competition between 
the perennials, which is an important factor in the survival of a species 
in the moister regions, is wholly lacking. It should be noted, however, 
that in the less extreme deserts, as in the vicinity of the Desert Laboratory, 
competition exists between plants, although this is not at first apparent. 
In this case the competition is not for room, but for water, and is not mani- 
fest by palpable crowding, but by invisible competition of the roots. Thus 
the reactions are with the physical environment and are exhibited in a 
variety of ways, some of which concern the plants themselves in an inti- 
mate manner, being morphological and physiological, some being concerned 
with the flora as a whole. The environmental responses are often obscure 
and complex, but in other instances they are less obscure and apparently 
direct. 



GENERAL SUMMARY AND CONCLUSIONS. 67 

As is well known, a desert flora is in part perennial, lasting with but little 
outward change from season to season, and in part ephemeral, consisting 
of short-lived species which appear with the rains and which disappear 
with the return of the dry season. The ephemeral flora differs in no essen- 
tial regard from annuals of the moister regions; also, the environment to 
which they are exposed closely resembles the environment of the annuals 
of such regions. But the perennial desert flora, on the other hand, offers 
very striking departures from the corresponding flora of the moister regions, 
just as the environment to which they are exposed for the most of the year 
is also different. It will be sufficient, for the purpose of bringing out the 
point of view, to notice a few of the leading characteristics of desert plants 
and of their physical environment and, in a few instances, to observe pos- 
sible relations between the two. 

The most obvious features of desert plants are associated, in whatever 
way, with the subaerial portions. Leaves are usually greatly reduced or 
wanting, during the dry seasons at least. Spines are frequently present 
and the exposed parts are often well covered w4th hairs. The stomata 
are sometimes deeply sunken, the cuticle often very heavy, and a waxy 
substance may cover leaves or stems. The chlorophyll-bearing cells are 
arranged with the long axis at right angles to the leaf or stem surface. All 
or most of these characters are associated with the low humidity of the 
air. In certain deserts plants are also to be found with greatly enlarged 
stems and branches which serve as water-storage organs. It should be 
noted, however, that plants which do not have a constant surface undergo 
many marked changes with a betterment of the water relations, particularly 
if this comes when the temperatures are favorable. For example, many 
cacti organize leaves which are unsuited in structure for periods of extreme 
drought, and which consequently fall away soon after the close of the rainy 
season. These leaves enormously increase the rate of transpiration at a 
time when this is not injurious. 

It is not in the subaerial parts alone, however, that the plants of one 
desert are different from those of another, that plants are unlike in the 
same desert, or that plants of a desert are different from those of the more 
humid regions. The root-habits also exhibit not a little diversity and show 
marked reactions to the pressure of their environment. For instance, the 
desert shrubs of the region surrounding the Desert Laboratory at Tucson 
have well-marked root-systems, apparently constant imder natural condi- 
tions, which may roughly be designated as the tap-root type, the super- 
ficial type, and the generalized type. Other conditions being equal, species 
with characteristic root-types have also characteristic distribution, or 
exhibit in other regards consistent reactions. Thus, the widely extending 
and superficial type of roots is confined, among independent plants, to 
such as have water-storage capacity. The relation of this root-type to the 
distribution will be mentioned later. Plants wnth a dominating tap-root 



68 BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 

are confined to areas where the soil is relatively or actually deep, while 
species having generalized roots have a local distribution which may be 
considered the maximum. 

The relation of the superficial type of root-system to the distribution of 
the species is not so apparent in this relation in plants as with the other 
types of roots, but is undoubtedly close and possibly definitive. The ab- 
sorption roots of plants with water-balance mostly lie less than lo cm. 
beneath the surface and are thus subject to extreme desiccation for the 
maximum time, or in other words they are exposed to favorable moisture 
conditions the minimum time. How long the optimum water-absorption 
time may be for such species is not known, but that it is longer than might 
be supposed (from the period certain species can survive without water) is 
highly probable from the facts concerning their distribution. In brief, the 
best development of the fleshy species in question occurs where the rain- 
fall is periodic, occurring twice each year, and they are wanting or sparse 
where the rainfall is uncertain or occurs but once annually. Had these 
plants a deeply penetrating type of root-system the local as well as the 
general distribution would be very different from what it now is. Owing 
to the unfavorable character of the rainfall in southern Algeria, plants 
with a water-balance are wanting there, just as they are wanting in por- 
tions of southwestern United States where the amount or the character 
of the precipitation is likewise imfavorable. 

Besides the characteristics of the root-systems of the desert perennials 
whose significance has been sketched, there are other features of importance. 
For example, the roots lying near the surface bear tufts of delicate roots, 
which are formed during periods of active growth and perish when such 
seasons cease. By the organization of deciduous rootlets the absorption 
area of the species is enormously increased, and quickly, without at the 
same time increasing the distance of water transport. 

There need be mentioned here only one additional feature of the desert 
plants. It is now known, in brief, that the non-fleshy perennials of the 
desert, not halophytes, may possess a very dense cell-sap. This fact has 
been demonstrated in the subaerial parts of several species, and is assumed 
to hold for the roots also of the same species. As suggested, not all of the 
desert plants, however, are capable of developing dense juices. Thus, cer- 
tain fleshy species, and such mesophytes of the desert as have been studied 
in this connection, do not have more highly concentrated cell-sap than the 
ordinary plants of the humid regions. Further, it appears that desert 
species which, under natural conditions and during the dry seasons, form 
extremely dense juices, lose this capacity when grown under humid condi- 
tions. So far as is now known, species capable of developing a cell-sap 
with high osmotic power have generalized roots, although this may be of 
no especial significance; but the relation of this capacity to survival in an 
arid substratum is apparent and vital. 



GENERAL SUMMARY AND CONCLUSIONS. 69 

ENVIRONMENTAL FEATURES OF THE FLORA OF ALGERL\. 

The physical enWronment of the plants of southern Algeria is, in a few 
broad features, similar to that of the southwestern portion of the United 
States. These regions have about the same latitude, both are separated 
from a large sea by mountains, and the range in altitude is similar. There 
are other features, however, particularly as regards the amount and the 
distribution of the precipitation, in which the two widely separated regions 
are very unlike, and a correlated difference in the habit and composition 
of the floras of the two regions is apparent. 

The Algerian climate as a whole is a mild, temperate one, but very 
diverse. The latitude and topography taken in connection with the 
presence of large seas to the north and west, and a large continent leading 
away to the south are its chief determinants. The climate, therefore, of 
the northern portion is coastal; that of the southern portion continental. 

Probably the most important of the secondary factors which modify the 
climate of Algeria is its highly varied topography. An important mountain 
system, the Atlas, made up of many more or less detached groups and 
secondary systems, a plateau or steppe Ij^ng 3,000 feet more or less above 
the sea, and finally the northern edge of the Sahara, which has a very 
diverse topography of its own — such is the surface of Algeria. 

Algeria is divided into three climatic provinces corresponding to the 
leading topographical differences: the Tell, including the littoral, or por- 
tion between the maritime Atlas and the Mediterranean; the High Plateau, 
or steppe, which lies between the Tellian Atlas and the Saharan Atlas ; and 
the desert. These provinces have marked indi\4dual differences in rain- 
fall, temperatiure, and other climatic features. 

In the Tell and the High Plateau the mnds from the sea deposit most 
of their moisture. Along the coast as much as 700 mm. of rain is recorded, 
while in other parts of the Tell it is about 570 mm. On the High Plateau the 
yearly precipitation sinks to 310 mm. In the desert south of the Saharan 
Atlas, however, where the altitude is lower and the temperature greater 
than in either of the other provinces, the yearly rainfall is 200 mm. and less. 
In some years, in fact, no precipitation whatever is reported in the desert. 

The seasonal distribution of the rains in any arid or semi-arid region is 
of great importance as a factor in shaping the character of the vegetation. 
For example, in the semi-arid region of the southwestern part of the United 
States, in the Tucson region, there are two distinct rainy seasons — the rains 
of winter and those of summer — and here the plants uith a water-balance 
are an important feature ; but farther to the west, where there are no summer 
rains, there are no succulents. In Algeria, also, there is but one rainy season 
and it has already been noted that the absence of plants with water-storage 
facilities is one of the leading characteristics of its vegetation. The seasonal 
distribution of rains is as follows: In the Tell, in winter it is 42 per cent. 



70 BOTANICAL FEATURES OF THE ALGERIAN SAHARA* 

in spring 27 per cent, in autumn 27 per cent, and in summer only 4 per cent. 
On the High Plateau the percentages are 30, 20, and 34 for winter, spring, 
and autumn, and 16 for summer. In the desert the percentages for winter, 
spring, and autumn are 37, 39, and 20 respectively, while in summer 4 per 
cent of the entire rainfall occurs. On the High Plateau, however, and in 
the Saharan Atlas the distribution of rain is much more equable, since 16 
per cent falls on the High Plateau in summer and 13 per cent in the Saharan 
Atlas the same season. We have, therefore, the interesting result that both 
in the Tell and on the desert there is a long, dry summer season, but in 
the intervening country more or less rain falls at this time of year. It 
seems very probable that a careful study of the plants of these regions 
would show reflected in the vegetation this peculiar character of climate.* 

The mean relative humidity changes in a marked manner as one passes 
from the Tell, across the High Plateau, and enters the desert. For ex- 
ample, at Fort National the mean relative humidity is 85 per cent. On 
the desert it varies from 54.6 per cent at Ouargla to 42.6 per cent at In 
Salah, At times in midsummer the humidity in the desert is too low to 
measure with instruments ; it is often 7 or 9 per cent. On the other hand, 
the humidity in autumn is surprisingly high, ov/ing in part to the lower 
temperature and in part to the northerly winds. However, no dew is 
reported and probably its occurrence is rare. 

With so great difference between the Tell and the desert in relative 
humidity is associated marked variation in the rate of evaporation. For 
example, at Algiers the total annual evaporation is 1,654 mm., while at 
Ghardaia it is 5,309 ram., which is possibly the greatest amount of evapo- 
ration thus far reported. Thus, the difference in evaporation between the 
Tell and the desert is nearly as the ratio 4 to i . 

The evaporation-rainfall ratios for the Tell, High Plateau, and the desert 
are of great interest. The seasonal evaporation-rainfall ratio for the littoral 
is 2.5 to I ; that of the Tell is 3.5 to i ; that of the High Plateau is 9.4 to i ; 
and that of the desert is 46.5 to i. If we represent the evaporation-rainfall 
ratio as unity, the ratio for the Tell becomes 1.4 and the ratio of the High 
Plateau becomes 9 to 3.7, while the desert ratio is 18.6. 

The annual and daily variations of temperatures in the desert are nat- 
urally relatively great. At Algiers the annual variation is approximately 
40.7° C, while at Ghardaia it is 47.9° C. As great an annual variation as 
57° C. has been observed at Ghardaia. The daily variation of temperature 
is especially marked on the High Plateau and the desert, ranging 17° C. 
more or less on the High Plateau, and 20° C. more or less on the desert. 
These figures are occasionally overstepped: for example, at Batna in July, 
1904, when the maximum daily range was 21.8° C; and an observation 

* Plants with subterranean water-storage organs — bulbous plants — are said to be 
a feature of the High Plateau. 



GENERAL SUMMARY AND CONCLUSIONS. 7 1 

made by the writer in the open desert between Ouargia and Touggourt, 
in November, 19 10, showed a variation of temperature of 24.7° C. between 
3 o'clock in the afternoon and 6 o'clock the following morning. 

The absolute maximum temperatures in southern Algeria are fairly high. 
At El Golea, for example, they are 47°, 46.5°, 48°. and 49.2° C, while at 
In Salah, about 700 miles from Algiers, the maximum temperatures for 
four years have been found to be 50°, 49-2'', 5°°. and 48° C. It is interest- 
ing to note that at Ouargia, which is much nearer the coast than In Salah, 
even higher temperatures have been recorded. The maxima for as many 
years are as follows: 50.2°, 51.0°, 52°, 49°, and 48.4° C. Usually in winter 
freezing temperatures are experienced at all stations in southern Algeria. 

Very little has been done on the soil temperatures in the desert region, 
but at Ghardaia, in July, 191 1, the temperature of the soil 15 cm. beneath 
the surface of the soil ranged, maximum from 36° to 37" C, minimum 
from 31° to 33° C, giving an absolute range of 6" C. 

In addition to the rainfall, the evaporation, and the temperature, there 
is another important climatic factor which should be taken into account, 
but which can not be stated in accurate terms, i.e., air-currents. It is a 
matter of common experience that one rarely obser\'es a calm day on the 
desert, but that usually the wind, which is often of considerable force, is 
found to be blowing. This is unquestionably an important factor in raising 
the total of evaporation and therefore in increasing the arid conditions of 
this region. The winds which are most effective in the direction mentioned 
are those which come from the desert and are known as the ' ' sirocco ; ' ' 
these are most likely to blow in spring and summer, although they occur 
in auttimn also, and to a very limited degree in winter. When the winds 
blow from the north cooler conditions occur, the relative humidity is lower, 
and therefore the evaporation rate is less. The sirocco, or desert wind, 
crosses the Mediterranean and is sometimes felt in southern Europe. It 
does not generally last more than three days at one time, but at Batna, in 
July, 1902, it was reported for eight consecutive days. When the sirocco 
blows the humidity is likely to be markedly affected; for example, at Batna 
during the eight-day sirocco alluded to, the relative himiidity fell from 25.6 
to 16 per cent on the first day. 

SOME EFFECTS OF TEMPERATURE AND RAINFALL IN SOUTHERN ALGERIA. 

While it is recognized that, generally speaking, climate shapes the char- 
acter of the vegetation, its immediate effects can not well be measured, or, 
at least, have not been acciu-ately measured, so that it seems necessary to 
confine one's observations to supposed or probable effects, however unsatis- 
factory this may be. So far as suits the present purpose, climatic effects 
may conveniently be separated into those which are direct and those which 
are not direct, remembering at the same time that the division is purely 



72 BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 

arbitrary, since the climate is a complex of various factors and its effects 
on vegetation are also complex. Among the climatic factors whose effects 
are most striking are the air temperature and the rainfall, and only certain 
effects resulting from a variation of these will be commented on here. 

In parts of the Sahara visited where the most rain is reported, especially 
Laghouat and Biskra, plants were observ^ed to exhibit exposure preference. 
Here the south or southerly facing slopes may have a floral composition 
different from the opposite exposure. In each instance the soil condi- 
tions, and apparently the moisture conditions also, were alike. Exposure 
preference was not noticed in the southern portions of the colony. Another 
temperature relation was observed, namely, the renewal of growth in the 
autumn. This is probably direct effect, although the point is not certain. 
In Ghardaia it was seen that many of the perennials were taking on new 
growth and coming into flower, although no rain had fallen for 12 months. 
Analogous conditions, with a significant difference, occur each year in the 
Tucson region. Here with the change from a cooler to a warmer tempera- 
ture, as from \vinter to spring, or from spring to summer, fairly independent 
of the rainfall, many perennials organize flowers or shoots. But, so far as 
is known, no species renews its vegetative activities with the coining of 
winter, or with a decreased temperature and also independent of the rains, 
although there are characteristic winter and summer plants. Judging from 
analogy, therefore, it would appear that the stimulus to development on the 
part of the M'Zabite plants maybe from the relatively better water relations 
made possible by a lower temperature without rain. In November at Ghar- 
daia the evaporation rate is much below that of summer, that during the 
night being very small. Further, it was told me by good authority that the 
same species seen growing in autumn renew growth whenever rain chances to 
come, whatever might be the season. But it should be remembered that 
rain most commonly occurs in this region in winter, so that the plants may 
have a rhjrthm to which they usually conform, but from which they may 
depart, and that both stimuli (better water relations and lower temperature) 
are the annually reciirring factors by which it may have been induced. 
Reference, of course, is made to perennials only, as no annuals were seen 
until the rains of spring made conditions favorable for their appearance. 

The effects of a varying amount of precipitation are naturally the most 
marked of any climatic factor. It is especially striking as one goes south 
from the Mediterranean, crossing the Tell and the High Plateau and enter- 
ing the desert proper. Whether the effects would be increasingly striking 
vnth. deeper penetration of the desert is doubtftd. As is well known, a lead- 
ing characteristic of the vegetation of the littoral and of the Atlas Moun- 
tains is the presence of forests of whatever species. As the littoral is left 
behind the forests disappear until on the High Plateau there are only strag- 
gling trees along the dried water-courses. This steppe bears mainly shrubs. 



GENERAL SUMMARY AND CONCLUSIONS. 73 

many of which are halophytes, with the perennial grass, Siipa tenacissima, 
and Artemisia herba-alba away from salt spots. Such low forms are present 
in sufficient numbers as to give character to the landscape and to conceal 
the surface of the ground fairly well. 

South of the Saharan Atlas a marked change occurs. Here, with a rain- 
fall of 200 mm. and less, the trees are confined to the dayas, a narrow belt, 
the vicinity of oueds, and the oases, exclusively. The shrubs of the hamada 
also decrease in numbers as one goes south, and where the annual precipita- 
tion is least, as on the Gantara between Ghardaia and Ouargla, large barren 
areas extend. At no place on the hamada of the M'Zabite region are the 
shrubs present in sufficient numbers or size to conceal the surface of the 
ground or to give character to the landscape. 

Aside from the effects following a lessened annual precipitation there is 
also to be taken into account the increasing uncertainty of rain, or its irregu- 
larity, which is also a marked characteristic of the Saharan climate. In 
the desert, also, storms are likely to be of the torrential type. I did not 
observe vegetation characteristics which appeared directly traceable to 
the irregularity in rainfall, but Hayw^ard reports an interesting condition 
observed by him in the southern Sahara, near Kidal, where large tracts of 
Mimosa had died from an unusually long period (five years) without rain.* 
It is not at all improbable that to the cause named much is directly trace- 
able which is generally attributed to insufficient rainfall taken in the usual 
sense. It is probable that the vegetation of the desert — the amount as 
well as kind — is due to the capacity of desert forms to meet successfully 
the occasional, even rare, conditions, of whatever sort. 

THE SOIL RELATION IN SOUTHERN ALGERIA. 

A very important environmental factor, although one which can not at 
this time be adequately presented, is the soil relation. Nowhere is the 
edaphacic factor more important than in the desert, where quantity and 
quality are always important and occasionally even determining factors. 
In this connection I do not refer particularly to dunes or to chotts, but to 
country soils, that is, the sort most commonly to be found, which in south- 
ern Algeria is a clay with sand present in greater or less amount. So far 
as the relation of plant to soil refers to the presence or the absence of the 
plant, the problem can be briefly stated thus : Given similar kinds of soil 
and an equal precipitation, areas where, within limits, there is greatest 
depth of soil will have the largest number of plants, and areas with hght soil 
covering will have few or no plants. Also, having given sufficient soil, the 
kind of plants present, together with certain root-types, will depend on the 
soil depth. It should be understood that these generalizations are supposed 
to apply to southern Algeria and not the deserts in general, or at least not 

* Through Timbuctu and across the Great Sahara, 1912, p. 266. 



74 BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 

to semi-deserts where in certain regards a very different condition obtains. 
The plant distribution thus dependent on soil depth, and the root character 
also having relation thereto, will be presented below ; the soil conditions, so 
far as they are known to me, can be given briefly in this place. 

From a few excavations on the hamada near Laghouat, on an analogous 
area by Tilrempt, on the hamada at Ghardaia, between Ghardaia and 
Ouargla (Gantara), and by Biskra, in each instance with analogous topo- 
graphical conditions, it was learned, in short, that on formations of this 
sort the soil is usually less than 50 cm, in depth, although where there are 
rocks or in drainage depressions the depth may be greater. In the oueds, 
where a different type of soil occurs, greater soil depth is naturallj'- found; 
also on the reg, or alluvial plain, frequently at least the fiood-plain of oueds, 
the soil conditions are peculiar and the soil is deeper than on the higher 
hamada. The special significance lies not so much in the differences in the 
soil per se, but in the differences in the water relation occasioned by varia- 
tion in depth. Owing to want of data in regard to penetration of water and 
its retention on the Algerian soils, the soil-moisture relation can only be 
gathered from inference. As regards rains, it is probable that light showers, 
those so slight as not to penetrate over 1,0 cm,, have little or no direct influ- 
ence on the perennial vegetation, but greater penetration directly benefits 
such plants. The first conclusion is drawn from the observation that fila- 
mentous rootlets (seemingly like the deciduous rootlets of the perennials of 
the Tucson region) on Haloxylon at Biskra were not found nearer the surface 
than 8 cm. Should the more superficial soil layer be moist for any con- 
siderable time, there would apparently be no reason why such temporary 
rootlets should not be formed nearer the surface. However, should there 
be sufficient moisture in the soil to permit absorption by roots, provided a 
slow rate was adequate to replace the transpiration loss, which rate was 
made lower by a more moist air, a sHght rain would be of great significance, 
even if it did not penetrate to any appreciable depth. On the intensely 
arid desert such shght modifications of the water relations as the lowering 
of the temperature as winter approaches, causing decreased evaporation 
or rains, although actually small in amount, may be of large moment to 
plants. Such a condition was noted at Ghardaia,* where there had been 

* Soil samples were taken from the plain about 3 kilometers north of Ghardaia from 
an area where the vegetation is relatively good (see p; 40). The surface of the soil at 
the place is slightly depressed. Soil samples from the depressed area and samples 
from portions of the plain adjacent to it were settled under water, with the result that 
the proportion of fine soil was found to be less in the depressed area. Samples of the 
soil from the lower area were placed in air-tight cans and the moisture content deter- 
mined subsequently. The soil was found to contain 0.8 per cent water. Through the 
kindness of the Bureau of Soils, U. S, Department of Agriculture, the critical moisture- 
content of the same soil was determined, which was 5 per cent. The critical moisture- 
content of mesa soil, taken from the creosote-bush slope at the foot of Tumamoc Hill, 
Desert Laboratory, as determined by the Bureau of Soils, is 10.5 per cent, which forms 
an interesting comparison of nearly similar situations. 



GENERAL SUMMARY AND CONCLUSIONS. 75 

a drought for over twelve months, but on the return of the cool season, 
with a lower evaporation rate, growth was resumed and several plants 
came into flower. This appeared to be not wholly the stimulus of lower 
temperature, since I was informed by good authority that the plants 
renewed their various activities whenever rains chanced to come, what- 
ever might be the season. 

From the observations last given it appears that sufficient moisture per- 
sists in the soil to tide perennials over the long periods of drought, although 
not in sufficient amount to permit active growth during the dry seasons. 
This is not an uncommon occiurence with desert plants. For example, 
whenever in the Tucson region the arid seasons are uncommonly long, or 
there has been a relatively small rain, as 25 per cent less than usual, much 
of the vegetation may remain dormant. Under such conditions an ever- 
green like Covillea tridentata drops all save the youngest and smallest leaves 
and maintains this nearly defoliate condition for long periods, with little 
other change. The plant behavior noted is always connected with insuffi- 
cient moisture. 

The soil in the oueds and probably also in the reg, as well as that of the 
dayas, is of considerable depth. The soil depth, or rather the depth before 
solid rock is encountered in the valley of the Oued M'Zab at Ghardaia, 
is from 20 to 30 meters, or even more; at the Daya Tilrempt the depth to 
water in one of the wells is about 95 meters. Although there is much gravel 
and sand in the fill of these depressions, it is likely that they afford the 
m.ost favorable soil conditions in the desert for the development of a large 
root-system. Be that as it may, it is certain that large plants, such as 
Tamarix and Pistacia, occur only in such places. 

Where there is most soil on the hamada, as in certain pockets near the 
old hill town of Ghardaia, abandoned several centuries since, one finds 
also the most and largest plants of this, the hamada, formation. Moreover, 
at the time in November when growth was noticed in the oued plants, it 
was also taking place in these favoring situations, about 50 meters above the 
level of the valley of the M'Zab and much above any possible permanent 
water-supply such as is afforded by a water-table. 

The various habitats, therefore, not including the oases, are naturally 
closely associated with soil differences. These are few and, in nearly each 
case, to name is sufiicient definition. There are dunes (areg), hamada or 
stony desert, reg or alluvial desert, the daya, and the flood-plain of the 
oueds (reg?). Modification of the hamada, reg, and oued flood-plain occurs 
whenever white hard-pan (caliche) is present. The soil of the reg, often 
that of the oued flood-plain and that of the daya, is fine alluvial and is rela- 
tively or actually deep. The hamada has the poorest soil condition, being 
underlaid by rock, and often or always by hard-pan as well. Large stones 
and boulders are embedded in the soil or lie on the surface. A modifica- 
tion of the hamada occtirs whenever sand is strewn over its surface, even 
6 



76 BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 

if the sand is only a few centimeters in thickness. This acts as an effectual 
mulch, increasing the retentive capacity of the soil, and very strikingly 
changes the character of the vegetation. The final habitat to be mentioned 
is the salt spot, or chott, where gypsum constitutes an important salt. 

As regards their relative importance the habitats in southern Algeria can 
probably be grouped in the following sequence, a relation which very pos- 
sibly holds good for the Sahara taken as a whole: Hamada, dune, oued, 
flood-plain, reg, daya.* 

The habitats are unlike as regards the relation to the rainfall and its 
effects. This is in part due to the differences in soils, or their depth, and 
in part to topographical differences. By the latter the low-lying areas 
receive a relatively large amount of water; and since their soil is relatively 
deep the water is retained longer than on the hamada, for instance, where 
the soil is shallow. 

The habitat preferences of the plants of southern Algeria are marked, 
as would be expected from the striking differences in the habitats. On 
the dunes, for example, we find drinn {Aristida pungens) as possibly the 
most commonly occurring and the most widely distributed sand-plant. One 
finds on sandy areas also Tamarix sp.. Euphorbia giiyoniana, Ephedra sp., 
Retatna retain, Limoniastrum guyonianum (zaita) , and other forms in smaller 
numbers. On the oued banks there are Tamarix, Nerium oleander (Lag- 
houat), and, near the oases, date palm and other introduced plants. On 
the flood-plains will be found a large number of species, among the most 
typical of which are Peganum harmala, Retama retain. Ephedra, Genista 
sp., and Haloxylon sp. The typical plants of the dayas are Pistacia atlantica 
and Zizyphus lotus, the latter occurring on flood-plains and the reg as well. 
On the chotts we find mainly such halophytes as Anabasis articulata, Hal- 
ocnemon strobilaceum, Salsola sp., Limoniastrum guyonianum, and others. 
The flora of the reg, so far as my observations show the conditions obtain- 
ing, is essentially like that of the flood-plains, which would be expected 
from the relation of the two habitats. South of Biskra, however, where 
the reg is probably not of fluvial origin, one finds a forest of Zizyphus lotus, 
and much Ephedra sp. among the most striking forms. Finally, the flora 
of the hamada, which has a peculiar stamp, can be briefly characterized. 

On the hamada are to be found the fewest species and the smallest indi- 
viduals. Probably most perennials of the hamada are under 30 cm. in 
height. Among the species characteristic of the hamada are Artemisia, 
Teucrium, Deverra, Centaurea, Acanthyllis, Thymelcea, Echinops, Henophy- 
ton, and Haloxylon. The last named is possibly the most widely distributed, 
occurring in other habitats as well. 

* The mountains have been disregarded, since in southern Algeria they are nearly 
barren. The only exception to this that I saw was that of the crustaceous lichens in small 
numbers at Ghardaia. In the central Sahara, however, where the mountains are of 
great elevation, the mountain climate brings about favorable conditions for plant life. 



GENERAL SUMMARY AND CONCLUSIONS. 7/ 

ROOT-CHARACTERS AND SPECIES DISTRIBUTION IN SOUTHERN ALGERIA. 

The general principles bearing upon the relation between the type of 
root-systcm and the distribution of the species, as observed in southern 
Algeria, can be briefly stated. Often the relation is close and apparent, 
but not always. For example, large perennials, such as Tamarix and 
Zizyphus, have an obligate specialized root-system, with a long tap-root. 
These plants naturally occur where there is considerable depth of soil, and 
hence are not to be found on the hamada, for instance, where it is shallow. 
On the other hand, such species as have a generalized root-system, like 
Acanthyllis and Haloxylon, are to be found on the hamada, but they occur 
also in other habitats where the soil is deep. The last type of root-system 
is flexible, accommodating the species to a wide range of soil conditions. 
In doing this the change in form is almost a change in type; for example, 
the roots of Haloxylon on the hamada at Ghardaia develop both laterals 
and a main root, but in deeper soil, as at Biskra and Ghardaia also, the 
laterals are nearly suppressed and the tap-root is the striking feature. A 
marked exception to the rule that plants with a generalized type of root- 
system have also the widest local distribution lies in Peganum harmala, 
which, ha\dng roots of this character, is nevertheless restricted to habitats 
where the soil is deep. The species is a half-shrub, having a perennial 
subterranean portion and a short-lived subaerial portion, the life of wliich 
appears to depend on the character of the water-supply. As learned by 
Fitting, the species can develop in its leaves a very dense sap, enabling 
it to extract water from a very dry soil.* In spite of this fact it appears 
to act like an annual in certain regards, requiring at all times, particularly 
during the most arid season, a relatively good water-supply. 

Thus, in brief, a study of the relation of the root-type of the Algerian 
plants to the plant's distribution leads to the same general conclusion 
already obtained by similar but more extended study in the Arizona desert, 
namely, that the cormection is often a very close one and often of definitive 
importance. Where the root-type is an obligate type the distribution of 
the species is much restricted, but where it undergoes modification with 
changed environment the distribution of the species is much less confined. 
It is of interest to note especially that as a rule it is the latter kind of root- 
system that is developed by such plants as occur where the soil conditions 
are most arid, that is, on the hamada or its equivalent, and not the former, 
from which it follows that the generalized type of root-system is really the 
xerophytic type par excellence, and not the type with the most deeply 
penetrating tap-root, as might be supposed. 

* Die Wasserversorgung und die osmotischen Druckverhaltnisse der Wiistenpflanzen. 
Zeitschr. f. Botanik, 4, 191 1. 



78 BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 

THE BIOTIC FACTOR. 

It will be well to summarize some of the main facts regarding another 
and important environmental feature of the Saharan plants, namely, the 
relation to herbivorous animals. In the western Sahara, wherever there is 
any forage, animals which subsist on it are to be found. Of the wild animals 
the gazelle is probably the most nimierous and the most destructive. All 
travelers across the desert have noted the presence of this animal. In the 
northern Sahara Tristram remarked its abundance fifty or more years ago, 
and it may be frequently seen by the traveler at the present time. In 
addition to the native animals, the domestic animals, especially the sheep, 
goats, and camels, are very numerous, very destructive of plants, and range 
great distances for food. As a result, an area around every well or oasis, 
extending as far as 40 kilometers or even much more than this,* is repeat- 
edly grazed over and has been utilized in this manner for centuries. As a 
result only the poisonous or the distasteful species, or the plants especially 
well armed, are left undisturbed to grow and reproduce, while the balance 
are more or less consumed, frequently so much so as to be quite unrecog- 
nizable. From the large number of camels, sheep, and goats which range 
the desert pastures it might be concluded that the leading types of plants 
to be found v/ould be such as are not eaten by them, but this is not the 
case. On the other hand, possibly the most generally consumed form is 
Haloxylon, which grows on the oued flood-plain, the reg, and the hamada. 
Thus, so far as this type is concerned, there is probably little or no diminu- 
tion in numbers because of the attacks of animals. 

A similar conclusion would doubtless be drawn after study of other forms, 
but there lies at least one notable exception, namely, the influence of animal 
grazing on the distribution of the betoum {Pistacia atlantica) . The betoum, 
which is the largest arboreal species in the Sahara, is confined to the region 
of the Dayas; that is, to the country immediately south of Laghouat. The 
tree is unarmed and is eagerly sought after by all herbivorous animals for 
its foliage and tender twigs. Owing to the presence of such animals, wild 
and domesticated, the young tree would have no chance to survive were 
it not that, growing in association with it, is the jujube {Zizyphus lotus), 
which is armed and is not eaten by any animals. The jujube affords safe 
protection for the seedling betoum, and in its capacity as nurse prevents 
predatory attacks by animals during the critical period. The survival (and 
probably the distribution as well) of the betoum is mainly conditioned on 
the presence of its protector. 

When I first visited southern Algeria it seemed improbable that any por- 
tion of it, or at least any portion that I should be likely to see, would exhibit 
the possibilities of plant growth as unaffected by herbivorous animals. 

* Hayward, loc. cit., p. 320, says that at In Salah camels are driven 200 kilometers 
before finding suitable grazing-grounds. 



GENERAL SUMMARY AND CONCLUSIONS. 79 

But finally there were found two classes of plant formations in which 
animals either had not intruded at all, or not to a harmful degree. One of 
these is the wide flood-plain of the Oued M'Zab, or one of its tributaries, 
lying about 50 kilometers east of Ghardaia. Despite the fact that the flocks 
are very numerous in the vicinity, and that the flood-plain is on the regular 
caravan route between Ghardaia and Ouargla, there are few signs of grazing. 
The entire plain is so well covered by shrubs that the vegetation gives the 
tone to the landscape — a rare thing in the desert. Here one finds Retama 
retain, Genista saharce, and Ephedra sp., as well as other species in fair 
abundance. Thus the plants are not only numerous, but are of a good 
size. It should be observed that on either side of the flood-plain, on the 
hamada, scarcely any vegetation may be found. 

The second formation referred to is that of protected areas, especially 
at Ghardaia, which have been little distiu-bed at any time, and portions 
of them not at all disturbed for centmies. These are the cemeteries. Such 
areas are situated not only in the floor of the M'Zab Valley, where the 
plant conditions are relatively favorable, but also on the hamada, where 
they are relatively very unfavorable. Both in the valley and on the hamada, 
as well as on the valley wall between the two wherever there chances to 
be soil, the plants are relatively nimierous and of fair size. This fact has 
been detailed under the section on Ghardaia and need not be more than 
mentioned here. 

From these two general observations (exceptions to the usual conditions) , 
that on the flood-plain of the Oued M'Zab and the cemeteries at Ghardaia, 
it is concluded that the grazing of animals has had a very marked influ- 
ence in modifying the flora of southern Algeria. So far as could be told 
from the limited opportunity to observe, the modification has gone along 
on at least two Unes, which are, of course, closely related. The size of the 
plants eaten is much under normal for the particular locality, and at the 
same time the capacity of the plant for reproduction has been greatly 
lessened. That such species as are not touched by animals have not spread 
more rapidly, or even have not become the dominant forms, is an interest- 
ing problem, and one that would have to be worked out for each species. 
It can be suggested, however, that the restricted distribution probably lies 
in the fact that the struggle of desert plants is mainly with an adverse 
physical environment rather than with one another, and that such condi- 
tions would not be affected by grazing animals. For example, large shrubs 
do not occur on the hamada, hence Tamarix, Zizyphus, and Rhus, as well 
as Peganum harmala, are limited to situations where the soil is fairly deep 
and the water relatively favorable. Euphorbia guyoniana also occurs only 
in sandy soil, and the number of plants limited in their distribution to soil 
characters is necessarily a large one. 



80 BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 

COMPARISON OF SOME GENERAL FEATURES OF THE VEGETATION OF SOUTHERN 
ALGERIA AND OF SOUTHERN ARIZONA. 

When we compare the most striking characteristics of the vegetation of 
the Algerian Sahara with that of the Tucson region where the Desert Lab- 
oratory is situated, we find some interesting differences, which may be 
summed up in the terms "desert" and "semi-desert," as appHed to the 
two widely separated regions. What is meant by these terms will be 
apparent from the following short characterization : 

Passing into the Sahara from the Saharan Atlas, over the route which 
I followed, one encounters a great variety of topography, of which the 
most extensive may for the moment be classed as plains. The plains are 
divided into three well-marked regions, that of the dayas, the Chebka, and 
the Gantara (hamada). The topography is iuither diversified by oueds 
and their flood-plains and by low, flat-topped mountains. On the northern 
portion of the plains one encounters a sparse population of low perennials, 
and as Ghardaia is approached the plains vegetation becomes continuously 
poorer until at Ghardaia there appears to be none. On the hamada be- 
tween Ghardaia and Ouargla areas are to be crossed, several kilometers in 
width, where perennials are wholly lacking. The decreasing plant popula- 
tion of the plains, until it entirely disappears, is entirely due to the increase 
in aridity as one goes from the mountains to and across the Ghardaia- 
Ouargla country. The low moimtains are almost entirely barren. The 
flood-plains of the oueds, however, support a surprisingly luxuriant popu- 
lation of perennials. 

Should we contrast the topography and vegetation of the Algerian Sahara 
with that of southern Arizona we would find little that is similar and much 
that is different. The wide-stretching plains (bajada) of southern Arizona 
are well covered with perennials of good size. The water-courses are fringed 
with trees, and often an open forest is to be found on the flood-plains. The 
low mountains have a fairly dense plant population, partly of trees, and the 
lower mountain slopes are often covered with a mixed flora of shrubs and 
trees. It may be said that there is probably no large area in southern 
Arizona, where the soil conditions are favorable for plants, where the water 
conditions are too meager to support a perennial flora of some sort. The 
greater aridity of the northern portion of the Sahara is evident, therefore, 
from the great contrast in its flora. 

In crossing the plains of southern Algeria one is Hkely to call a region 
barren when close inspection will show that this is not the condition. In 
fact, it was foimd that areas on the plain, i6 by i6 meters in extent, car- 
ried as many as 330 or more perennials, although a casual glance did not 
reveal the presence of any conspicuous vegetation.* Both of these condi- 

*It should be understood that such densely populated areas are separated by wide 
stretches where are few or no plants. 



GENERAL SUMMARY AND CONCLUSIONS. 8 1 

tions are the immediate result of the small rainfall. The reason for the 
large number of plants in certain areas, as above noted, lies in their small 
size, since it would probably be difficult to find an equal number on this 
area were the plants as large, for example, as in southern Arizona. The 
fact that the perennials are inconspicuous is in part because they are small 
and in part because the leaves are either absent or greatly reduced. 

When viewed somewhat more closely, one finds other features in which 
the flora of southern Arizona and of southern Algeria are unlike. Travelers, 
botanical as well as non-botanical, have described the armed condition of 
the Saharan plants until the impression is general that such plants as per- 
sist from season to season are usually well provided with spines. What may 
be the proportion of armed to unarmed plants in the northern Sahara I 
do not know, but to a person familiar with the plants of southern Arizona, 
where spinose forms are very numerous, the Algerian plants do not appear 
especially well protected. As this appears to be a general condition, it is 
scarcely an accident that the spines of the American species of the genus 
Zizyphus, for example, are much better developed than are those of the 
Algerian representative of the same genus. From the circumstance that 
grazing by wild as well as by domestic animals is very destructive in Algeria, 
apparently more so than in Arizona, where the results of grazing are scarcely 
to be noted, the general facts regarding spininess in plants, as given above, 
suggest the really small influence such animals play in shaping such a 
character in desert plants. 

Finally, it need only be remarked that plants with a water-balance are 
wanting in southern Algeria, and that they constitute one of the striking 
features of the flora of the southwestern United States. 



$. 



T^ 




i^jgjfpiA' .>: u^y^ar^ 



) > 

Fig. 4. Shool-Viabil o( AcanthylHs tragacanthoides. 

Laohouat. 




Fig. 5. Slifinl-habit o( Zollikoferia spir 
Laghouat. 



I./,4^ i-: 











Fig. 7. Zollikoferia spinosa in habitat, plain (hamada). Laghouat. 



M 



- . ^ *i< 



'/■^' 



■^^-(i^'^'r^f 'fci-- 



iig. 6. Detail of norili t]u| 









^y^: 




iJiad iVjouiilaiiis vvlicrc ^.onjKoiii ]:i spinosa is 



the dominant species. Laghoual. 







Haloxylon articulatum. 










^ 



Fig. 10. The Daya of Tilrempt from the plain, showing the character of the depression. 




Fig. 1 1 . Near view of the Daya of Tilrempt. The (orlified stage station, bordj, and a nomad camp are to be 
seen. The flattened, level, lower surface of the trees is the effect of gramng, mainly by camels. 



iki ^ 








■ f 








■•:S<..-^v '^ 



^k^:^ 



bfloum (Pislacia) at the Daya of Tili 



CANNON 



r^^^ sf' 










Fig. 13. A young specimen of betoum in the midst of a protecting jujube, at the Daya 

of Tilrempt. 




Fig. 14. Leaf and shoot habit of the jujube Fig. 15. Leaves of the betoum (Pistacia atlantica), 
(Zizyphus lotus). Daya of Tilrempt. from the Daya of Tilrempt. 



CANNON 




S^-^ 



t;^-;;- -^y'.-t ;, 






•^*^!^"f^^*^ r ••?Ve-. 



V^' 



Fig. 16. Souili wall of the valley of the Oued M'Zab at Ghardaia. 







Fig. 17. Detail of an eroded bank of the Oued M"Zab at Ghardaia. The overhanging stratum is 
hardpan similar to the "caliche" of southwestern United Slates. 



CANNON 



PLATE 7 




Fig. 18. Shoot-habit of Haloxylon aiticulatum, from the plain near the Day a of Tilrempt. 








1 .1 The fields are divided into plots about 3 by 4 feet in size, 
tor the more economical use of water. Young barley is shown growmg (November). 



CANNON 



PLATE 8Q 



T'm 









M^Sf^Mb. 








Fig. 20. Vegetation in upper part of a "draw" on plain north of the M'Zab Valley' Ghardaia. 







iflBtfc-^ 






'i^/ 



Fig. 21. Situation of square No. 2. on plain north ot valley at Ghardaia. 






CANNON 



PLATE 9 




Fig. 22. Capparis spinosa at base o( ,^..^j ... 



m 



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^.^.iat* 



5i 




.^j 



Fig. 23. Leaves of Capparis spinosa. from Ghardaia. 






Fig. 24. Leaf-habit of Daemia cordata. Ghardaia. 





«rv. 



I \ \v' i ■•11 f 







Fig, 25. Shoot-liabil of Salvia cegyptica. Ghardaia. Fig. /b. L pi'Cr surface of rocks, showing small 

incrusting lichens, on a low mountain about 
5km. north of the M'Zab Valley, Ghardaia. 



CANNON 



PLATE 11 







1 '^- -*' -:. . ' ^ax •<* •»*"' 












«- - ^JS" 



'kr-y^-.^x 



Fig. 27. Habitat of Peganum harru.iL;, ... 




Fig. 28. Shoot and leaf habit of Peganum harmala, from Ghardaia. 



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•i 



^^feV'^vv^: 



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Fig. 30. Leaf-habit of Henophyton descrti. Ghardaia. 



CANNON 




Fig. )\. \'ir\v ir. a ccmclciy nl Lii 



Ir. show tin- ic!a',nxi\- ahuiK 




BA*^' 



,i=ry»-^- 








Fig. 32. View in an M'Zabite cemetery, Ghardaia. Haloxylon articulatum is the leading species shown. 




Fin.. 33. Habit of Devcrra scoparia, from plain about 3km. north of M'Zab 
Valley, Ghardaia. 










Fig. 34. Root-habit of Gymnocarpos frutlcosutn, from plain about 3km. north of 
M'Zab Valley at Ghardaia. 



CANNON 



TLATE 15 




Fig. 35. Root-habil ol a malurc specimen of Peganum harmala, from the floor of the M'Zab Valley 
neai Ghardaia. The soil at the place is comparatively deep. (See text for further explanation.) 




Fig. 36. Root-systems of Helianthemum sessiliflorum (right), Haloxylon articulatum, Bnd NolleUa 
chrysocomoides (left), from the flood-plain of the Oued M'Zab. Ghardaia. 



CANNON 



PLATE 16 




Fig. 37. Shoot and toot habit of Cilrullus colocynthis. Oued M'Zab, Ghardaia. 



i-^*' *• ASr'' 'i^f''^^2^.' ■ *•'». 



■ ,v--.-jv; 



--*•..•' .- .ti^ V,-« ->• .' '^^-^ ■■/»."■■ ■' 



tT- 



j^v: 






-- 


-fi5- 


^^^ 


:.vj«f-;!^ . 


-' l.^ 


r^Jtfe 


^ 


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: -f-^ 


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-:•■?= - 




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.^' ' 


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^ ■ 






:V.\ - 


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•>..; 


•■• ld~ -' 


-•/,'- 








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■>/ 


'^' 


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Fig. 3b. Euphorbia guyoniaua, in the valley ot the Uued IVl /.ah .-.i L.i.araaia. 



CANNON 



PLATE 1 7 




Fig. 39. Habit of Euphorbia guyoniana. Ghardaia. 





Fig. 40. To the left, shoot of Centaurea sp., showing effects of grazing; to the right, 
shoots of Teucrium pseudo-chamaepitys. From Ghardaia. 















«^i 



Fig. 41. Habit of Salsola sp. (below), and Echinopsilon muricatus, from the M'Zab Valley, GHardaia. 









'-• ,■.■•^.'^.• 



1 ..•'"--?.'" t^->^ ■*»-"* 















Fig. 4/. Lihardaia to CJuargla. Vie\N overlooking the liamada about 28km. Iioni dhardaia. 1 hr relatively 

abundant vegetation is associated with a light cover of sand over the area shown. The leading 

species are Aristida, Deverra, and Haloxylon. 



CANNON 



PLATE 19 



••V \^ ■; 



' ^' 







Fig. 43. Rctama retam, in dunes about 3cKin. iiom onaruaia 




Fig. 44. Dates at the bordj Zolfana. about 58km. from Ghardaia. One of two wells encountered 

between Ghardaia and Ouargla. 




ii*Cj^ 



■ys^' 






i<tl 




Fig. 45. Ghardaia to Ouargla. View overlooking flood-plain of the Oued M Zab. or a tributary 
of this oued. The adjacent upland is apparently without plant life. 



CANNON 



PLATE 20 



-Ji-' 






" WV^ 



:vt^.*i 



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e^^^' 



i;^'-.i-.- 



■^ 




if^' 



Fig. 46. Vegetation on edge of the Oued M'Zab, about 63km. east of Ghardaia, showing 
habitat of Rhantherium adpressum in foreground. 



»s "/oVi( 








Fig. 47. Sandy Hood-piain of the Oued M'Zab, about 63 km. from Ghardaia. Ketama, Genista 
and Ephedra are the leading plants in this place. 



PHP 







Fig. 48. Habit of Ephedra alata in habitat shown in figure 47. This specimen was 1.5m. high. 




:^*t.. 



v'vM' 









-"^ -^ - 



. -.• ..4- ' • K< 






^- ^: ■■^■v;■ 



Fig. 49. View of habitat of Ephedra alenda, 138km. from Gliardaia. 




.;■' , ' -5*.. '■ . . A ,^ 

Fig. 50. Detail of suckering habil of Ephedra alenda, from habitat fhown in hgure 49. 



CANNON 




hig. 5 1. Vegetation, mainly Ephedra and Retama, of the western edge of the v^nou ivieijaiu. 





-:^0^ 



Fig. 52. Approach to western edge of the Chott Mellala, showing characteristic rounded hills, or mamelons. 



CANNON 



PLATE 23 




' ti'^il^ -■ ~'Xf- - •*• 



^ 



Fig. 53. Vie\ 



he- Ouar^la plain aixi tli< C l.cli '\; 
appearance of eroded hills. 



Jerishc 









Fig. 54. Looking toward the Uuargla plain (reg). 




. . I' iflTlM'fcTi' '^ 
Fig. 55. Shallow well about 25km. north of Ouargla. 




Fie. 56. Ou. 



leaves is covered with an incrustation ot salts. 







Fig. 57. Habit of Limoni 



About 25km. north of Ouargla. 



:annon 



PLATE 25 







Fig. 58. Vegetation of the reg. desert, about 25km. north of Ouargla. Ephedra and Retaraa 
are the leading species of the area a spreading dune. 




Fig. 59. Shoot-habit of Halocnemon strobilaceum, about 28km. north of Ouargla. 






.^.. 




^mii!fi^. 




vd-M^,.* 



hig. bU. Habil ot Halocnemon strobiiaceum, on ihc edge ol a cholt, about ZOkm. north ol CJuargia. 




Fig. 61. Shoot and leaf habit of Anabasis articulata, about 32km. north of Ouargla. 




Fig. 62. Detail o( the shoot-habit of Salsola tetragona?, about 25km. north of Ouargla. 



*/tt¥*^- 



-^jsoak 



N^ 



m^ 









we 











-■..■jiWW'ru 



Fig. 63. Habit of Nolletia chrysocomoides near the edge of a chott, about 80kin. north of Ouargla. 



PLATE 28 




Fig. 64. Tamarix sp. as a sand-binder near Bled-el-Amar, south of Touggourt. 




•^a*. 



Fig. 65. Biskra Habitat oi Euphorbia guyoniana, looking toward the Ujebel Maouya. with the Chaine de 

Sfa in the background. 



CANNON 










Fig. 66. Characteristic vegetation on the north slope oi the Djcoci bou ivKcial, LiisKra. 
Haloxylon scoparium is a prominent species. 




^Sfti- 












4^ 






^-::^.>t5 











Fig. 67. North base of Ed Delouatt hills, west o( Biskra, showing the low-tacing aunes. 
To the right is a glimpse of an oued which pierces the hills in the middle distance. 



PLATE 30 




^-.->'>;V--r:. xr-:^ 









Fig. 68. Flood-plain of the Oued Hamman es Salahin, Biskra. Halopli>i 
species occupy the foreground. 
















»..-_^ -J < / 




#.^ 






Fig. 69. Habitat of Phelypaea violacea shown in hgure 70. 



CANN 




Fig. /U. Young shoots ot Phelypasa violacea, at Fig. 71. Habit of young specimens of Phelypaea. 

north base of Ed Delouatt hills, Biskra. Except for about 15 cm., plants were buried 

1,V .an.!. BM;,;,. 










Fig. 72. Aspl.odclus sp. at nortli base oi Ld Delouatt MW. I 4 wi. t'hotographeil ir. IMar.i 



CANNON 



Ol ATP QO 





^i^y^ 



,^.j.«*; 






::-.*rj^^-0- 






v^'^>-- 



■;.-:^: 



'* ;♦ 












hig. /4. Vegetation ot north slope ot the low hills which are north ot Biskra, herula vescentensis is 

the perennial appearing in the figure. 



CANNON 




square No. 2, near area shown in fig. 74. Ferula and Haloxylon are the leading species. 




Fig. 76. Koot-habit of Haloxylon scoparium, 
from a wash near Biskra. 



Fig. 77. Young shoots and mature roots of Ferula vescenicns 
North of Biskra. 



PLATE 34 




Fig 78. Root-habit of Fagonia growing on edge ot a wash. Biskra. 



Fig. 79. Large lateral root of Hal- 
oxylon, with numerous deciduous 
rootlets, DO longer funcbonal. 




taken from above, of Fagonia from the flood-plain of a small oued near Biskra 



CANNON 



PLATE 35 



^^m^- --^ 




Fig. 8i. Spring annuals, March 17th, on north slope of the Djebel Bou Rhezal, Biskra. 




Fig. 82. Root and shoot habit of Peganum harmala, Biskra. The main root is especially well developed 
although the species has a generalized root-system. (See text.) 



PLATE 36 










Fig. 83. Annuals growing with Peganum, near Biskra. 



%:^-' 






■^\k' 









..-:^v*:A....^ ' 






.;'. ■>;" 



><-V 






plants are rather numerous in the rock crevices and small washes of the mountains. 



r 



QK Gannon, i^^illiam Austin 

922 Botanical features of the 

^25 Algerian .Sahara 



BioMed 



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