FOOTNOTES:

PLATE 18Fig. 41. Habit of Salsola sp. (below), and Echinopsilon muricatus, from the M'Zab Valley, Ghardaia.Fig. 42. Ghardaia to Ouargla. View overlooking the hamada about 28km. 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.

PLATE 18

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

Fig. 42. Ghardaia to Ouargla. View overlooking the hamada about 28km. 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.

PLATE 19Fig. 43. Retama retam, in dunes about 58km. from Ghardaia.Fig. 44. Dates at the bordj Zolfana, about 58km. from Ghardaia. One of two wells encountered between Ghardaia and Ouargla.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.

PLATE 19

Fig. 43. Retama retam, in dunes about 58km. from Ghardaia.

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

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.

PLATE 20Fig. 46. Vegetation on edge of the Oued M’Zab, about 63km. east of Ghardaia, showing habitat of Rhantherium adpressum in foreground.Fig. 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.Fig. 48. Habit of Ephedra alata in habitat shown in figure 47. This specimen was 1.5m. high.

PLATE 20

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

Fig. 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.

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

PLATE 21Fig. 49. View of habitat of Ephedra alenda, 138km. from Ghardaia.Fig. 50. Detail of suckering habit of Ephedra alenda, from habitat shown in figure 49.

PLATE 21

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

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

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

PLATE 22

Fig. 51. Vegetation, mainly Ephedra and Retama, of the western edge of the Chott Mellala.

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

PLATE 23Fig. 53. View between the Ouargla plain and the Chott Mellala, showing characteristic appearance of eroded hills.Fig. 54. Looking toward the Ouargla plain (reg).Fig. 55. Shallow well about 25km. north of Ouargla.

PLATE 23

Fig. 53. View between the Ouargla plain and the Chott Mellala, showing characteristic appearance of eroded hills.

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

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

PLATE 24Fig. 56. Ouargla to Touggourt. Leaf-habit of Limoniastrum guyonianum. The surface of the leaves is covered with an incrustation of salts.Fig. 57. Habit of Limoniastrum guyonianum. About 25km. north of Ouargla.

PLATE 24

Fig. 56. Ouargla to Touggourt. Leaf-habit of Limoniastrum guyonianum. The surface of the leaves is covered with an incrustation of salts.

Fig. 57. Habit of Limoniastrum guyonianum. About 25km. north of Ouargla.

PLATE 25Fig. 58. Vegetation of the reg. desert, about 25km. north of Ouargla. Ephedra and Retama are the leading species of the area a spreading dune.Fig. 59. Shoot-habit of Halocnemon strobilaceum, about 28km. north of Ouargla.

PLATE 25

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

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

PLATE 26Fig. 60. Habit of Halocnemon strobilaceum, on the edge of a chott, about 28km. north of Ouargla.Fig. 61. Shoot and leaf habit of Anabasis articulata, about 32km. north of Ouargla.

PLATE 26

Fig. 60. Habit of Halocnemon strobilaceum, on the edge of a chott, about 28km. north of Ouargla.

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

PLATE 27Fig. 62. Detail of the shoot-habit of Salsola tetragona?, about 25km. north of Ouargla.Fig. 63. Habit of Nolletia chrysocomoides near the edge of a chott, about 80km. north of Ouargla.

PLATE 27

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

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

PLATE 28Fig. 64. Tamarix sp. as a sand-binder near Bled-el-Amar, south of Touggourt.Fig. 65. Biskra. Habitat of Euphorbia guyoniana, looking toward the Djebel Maouya, with the Chaine de Sfa in the background.

PLATE 28

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

Fig. 65. Biskra. Habitat of Euphorbia guyoniana, looking toward the Djebel Maouya, with the Chaine de Sfa in the background.

PLATE 29Fig. 66. Characteristic vegetation on the north slope of the Djebel Bou Rhezal, Biskra. Haloxylon scoparium is a prominent species.Fig. 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.

PLATE 29

Fig. 66. Characteristic vegetation on the north slope of the Djebel Bou Rhezal, Biskra. Haloxylon scoparium is a prominent species.

Fig. 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.

PLATE 30Fig. 68. Flood-plain of the Oued Hamman es Salahin, Biskra. Halophytes of various species occupy the foreground.Fig. 69. Habitat of Phelypæa violacea shown in figure 70.

PLATE 30

Fig. 68. Flood-plain of the Oued Hamman es Salahin, Biskra. Halophytes of various species occupy the foreground.

Fig. 69. Habitat of Phelypæa violacea shown in figure 70.

PLATE 31Fig. 70. Young shoots of Phelypæa violacea, at north base of Ed Delouatt hills, Biskra.Fig. 71. Habit of young specimens of Phelypæa. Except for about 15cm., plants were buried by sand. Biskra.Fig. 72. Asphodelus sp. at north base of Ed Delouatt hills, Biskra. Photographed in March.

PLATE 31

Fig. 70. Young shoots of Phelypæa violacea, at north base of Ed Delouatt hills, Biskra.Fig. 71. Habit of young specimens of Phelypæa. Except for about 15cm., plants were buried by sand. Biskra.

Fig. 70. Young shoots of Phelypæa violacea, at north base of Ed Delouatt hills, Biskra.

Fig. 71. Habit of young specimens of Phelypæa. Except for about 15cm., plants were buried by sand. Biskra.

Fig. 72. Asphodelus sp. at north base of Ed Delouatt hills, Biskra. Photographed in March.

PLATE 32Fig. 73. Detail of square No. 1, on low hills north of Biskra.Fig. 74. Vegetation of north slope of the low hills which are north of Biskra. Ferula vesceritensis is the perennial appearing in the figure.

PLATE 32

Fig. 73. Detail of square No. 1, on low hills north of Biskra.

Fig. 74. Vegetation of north slope of the low hills which are north of Biskra. Ferula vesceritensis is the perennial appearing in the figure.

PLATE 33Fig. 75. Detail of square No. 2, neat area shown in fig. 74. Ferula and Haloxylon are the leading species.Fig. 76. Root-habit of Haloxylon scoparium, from a wash near Biskra.Fig. 77. Young shoots and mature roots of Ferula vesceritensis. North of Biskra.

PLATE 33

Fig. 75. Detail of square No. 2, neat area shown in fig. 74. Ferula and Haloxylon are the leading species.

Fig. 76. Root-habit of Haloxylon scoparium, from a wash near Biskra.Fig. 77. Young shoots and mature roots of Ferula vesceritensis. North of Biskra.

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

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

PLATE 34Fig. 78. Root-habit of Fagonia growing on edge of a wash. Biskra.Fig. 79. Large lateral root of Haloxylon, with numerous deciduous rootlets, no longer functional.Fig. 80. Shoot-habit, taken from above, of Fagonia from the flood-plain of a small oued near Biskra.

PLATE 34

Fig. 78. Root-habit of Fagonia growing on edge of a wash. Biskra.Fig. 79. Large lateral root of Haloxylon, with numerous deciduous rootlets, no longer functional.

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

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

Fig. 80. Shoot-habit, taken from above, of Fagonia from the flood-plain of a small oued near Biskra.

PLATE 35Fig. 81. 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 35

Fig. 81. 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 36Fig. 83. Annuals growing with Peganum, near Biskra.Fig. 84. General view of the north face of the Djebel Bou Rhezal, Biskra. Apparently barren, plants are rather numerous in the rock crevices and small washes of the mountains.

PLATE 36

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

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

FOOTNOTES:[1]Kearney and Means, Agricultural explorations in Algeria, Bul. No. 80, Bur. Plant Ind., U. S. Dept. Agric., 1905.[2]A. Engler, Die Vegetation der Erde IX. Die Pflanzenwelt Afrikas. 1 Bd., 1910, page 902.[3]The seasonal distribution of rain (by percentages) is somewhat different from that given by Engler, which is given in the accompanying table.Season.Littoral.Tell.High plateau.Winter413645Spring273246Summer4711[4]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 El 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.[5]Unless otherwise stated, the climatological statistics given in this paper were taken or compiled from Observations Météorologiques 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 by multiplying by 0.737 (Meteorological Notes, J. I. Craig. Cairo Scientific Journal, vol. vi, May 1912).[6]At Touggourt, however, no rain was reported during the summer season of 1908.[7]Kearney and Means,loc. cit.[8]The Root Habits of Desert Plants. W. A. Cannon. Carnegie Institution of Washington Publication No. 131. 1911. This paper gives a descriptive classification of the main root-types in the deserts of the southwest, in which such a root as found inAcanthyllisis calledgeneralized, in distinction to roots like those of most of the cacti, orZizyphus, the former having a system wholly superficial and the latter a system wholly deeply placed, asspecialized. 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.[9]Compare the root-system ofH. scopariumat Biskra, p.64.[10]The most striking change in the general character of the vegetation which the traveler notices as he goes from the less arid to the more arid portion of southern Algeria is its decrease in amount. This occurs through dwarfing effects of whatever cause and through a decrease in the number of individuals. Within certain limits the results observed are to be attributed mainly to the first of these, since there is often a surprisingly large number of perennials on any given area. But in other and more intensely arid regions (as portions of the Arabian-Egyptian desert, and indeed a limited area on the hamada between Ghardaia and Ouargla) plants are wholly wanting. Whether such is generally the case on the reg or the hamada farther south in southern Algeria is not known.[11]Tristram remarks that it “seems that the larger wild animals have been rapidly decreasing in numbers and are in process of speedy extinction. Dr. Shaw, 150 years since, enumerates in his travels . . . five species of ruminants, which from his descriptions must be the bubale, the aoudad or wild sheep, the addax, and the gazelle, as well as the stag. . . . As the population has not increased, but rather retrograded, we can only surmise that the substitution of the flint and steel gun for the matchlock of the Bedouin . . . has been fatal in its results to all larger game.” It may be remarked that the French impose such restrictions on the Arab as regards the character of the guns he may use (only the army and certain officials of the government employing modern arms) that for the region visited Tristram’s description holds fairly well for to-day.[12]Statistique Générale de l’Algérie, 1908.[13]Un voyage botanique au Sahara, Bull. Soc. Bot. Belg., 1898.[14]Massart,loc. cit.[15]Joan’s Guide de l’Algérie et de la Tunisie.[16]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 extinct. He says “L’extinction du Pistacia atlantica présente le caractère, tout à fait exceptionnel, d’ètre uniquement l’effet du climat.” It will appear from what is said in this study regarding the effects 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.[17]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.[18]Les Oasis du Souf et du M’Zab, La Géographie, 1902.[19]Foureau, d’Alger au Congo par le Tchad, 1902, mentions having met with indications 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.[20]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, Melika, Beni Isguen, and Ghardaia. 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 established 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.[21]In 1908, according to the Statistique générale de l’Algérie, 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 hectares of grain under cultivation.[22]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.[23]Fitting (Die Wasserversorgung und die osmotischen Druckverhältnisse der Wüstenpflanzen, Zeitschr. f. Bot., 4, 209-275, 1911) 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 atmospheres, 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 elsewhere, so far as I know, doesPeganumgrow where the conditions are extreme, as might be concluded from the habit of the plant as given above.[24]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.[25]The Root Habits of Desert Plants,l. c.[26]Compare the root-system of the species at Biskra, p.64.[27]In the vicinity of Tucson (see The Root Habits of Desert Plants) is to be found a slender-stemmedOpuntiawhose 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. InCereus greggiithe subterranean 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.[28]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 ofParietaria debilisgrowing 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 1. (Root Habits of Desert Plants,loc. cit.)[29]The vegetation in the vicinity of Biskra is so well known that a sketch will suffice as a basis of comparison with the flora and conditions of plant life farther south.[30]Liste des plantes observées aux environs de Biskra et dans l’Aurés, Trabutet al., Alger, 1892.[31]Briefly the case is as follows (see The root systems of desert plants,loc. cit.):Opuntia arbusculagrowing 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.[32]Eine botanische Exkursion nach Algier and Tunis, Bericht der Senckenbergischen Naturforschenden Gesellschaft in Frankfort a. M., p. 76, 1910.[33]Plants with subterranean water-storage organs—bulbous plants—are said to be a feature of the High Plateau.[34]Through Timbuctu and across the Great Sahara, 1912, p. 266.[35]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 determined 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.[36]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.[37]Die Wasserversorgung und die osmotischen Druckverhältnisse der Wüstenpflanzen. Zeitschr. f. Botanik, 4, 1911.[38]Hayward,loc. cit., p. 320, says that at In Salah camels are driven 200 kilometers before finding suitable grazing-grounds.[39]It should be understood that such densely populated areas are separated by wide stretches where are few or no plants.

[1]Kearney and Means, Agricultural explorations in Algeria, Bul. No. 80, Bur. Plant Ind., U. S. Dept. Agric., 1905.

[2]A. Engler, Die Vegetation der Erde IX. Die Pflanzenwelt Afrikas. 1 Bd., 1910, page 902.

[3]The seasonal distribution of rain (by percentages) is somewhat different from that given by Engler, which is given in the accompanying table.Season.Littoral.Tell.High plateau.Winter413645Spring273246Summer4711

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

[4]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 El 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.

[5]Unless otherwise stated, the climatological statistics given in this paper were taken or compiled from Observations Météorologiques 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 by multiplying by 0.737 (Meteorological Notes, J. I. Craig. Cairo Scientific Journal, vol. vi, May 1912).

[6]At Touggourt, however, no rain was reported during the summer season of 1908.

[7]Kearney and Means,loc. cit.

[8]The Root Habits of Desert Plants. W. A. Cannon. Carnegie Institution of Washington Publication No. 131. 1911. This paper gives a descriptive classification of the main root-types in the deserts of the southwest, in which such a root as found inAcanthyllisis calledgeneralized, in distinction to roots like those of most of the cacti, orZizyphus, the former having a system wholly superficial and the latter a system wholly deeply placed, asspecialized. 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.

[9]Compare the root-system ofH. scopariumat Biskra, p.64.

[10]The most striking change in the general character of the vegetation which the traveler notices as he goes from the less arid to the more arid portion of southern Algeria is its decrease in amount. This occurs through dwarfing effects of whatever cause and through a decrease in the number of individuals. Within certain limits the results observed are to be attributed mainly to the first of these, since there is often a surprisingly large number of perennials on any given area. But in other and more intensely arid regions (as portions of the Arabian-Egyptian desert, and indeed a limited area on the hamada between Ghardaia and Ouargla) plants are wholly wanting. Whether such is generally the case on the reg or the hamada farther south in southern Algeria is not known.

[11]Tristram remarks that it “seems that the larger wild animals have been rapidly decreasing in numbers and are in process of speedy extinction. Dr. Shaw, 150 years since, enumerates in his travels . . . five species of ruminants, which from his descriptions must be the bubale, the aoudad or wild sheep, the addax, and the gazelle, as well as the stag. . . . As the population has not increased, but rather retrograded, we can only surmise that the substitution of the flint and steel gun for the matchlock of the Bedouin . . . has been fatal in its results to all larger game.” It may be remarked that the French impose such restrictions on the Arab as regards the character of the guns he may use (only the army and certain officials of the government employing modern arms) that for the region visited Tristram’s description holds fairly well for to-day.

[12]Statistique Générale de l’Algérie, 1908.

[13]Un voyage botanique au Sahara, Bull. Soc. Bot. Belg., 1898.

[14]Massart,loc. cit.

[15]Joan’s Guide de l’Algérie et de la Tunisie.

[16]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 extinct. He says “L’extinction du Pistacia atlantica présente le caractère, tout à fait exceptionnel, d’ètre uniquement l’effet du climat.” It will appear from what is said in this study regarding the effects 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.

[17]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.

[18]Les Oasis du Souf et du M’Zab, La Géographie, 1902.

[19]Foureau, d’Alger au Congo par le Tchad, 1902, mentions having met with indications 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.

[20]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, Melika, Beni Isguen, and Ghardaia. 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 established 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.

[21]In 1908, according to the Statistique générale de l’Algérie, 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 hectares of grain under cultivation.

[22]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.

[23]Fitting (Die Wasserversorgung und die osmotischen Druckverhältnisse der Wüstenpflanzen, Zeitschr. f. Bot., 4, 209-275, 1911) 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 atmospheres, 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 elsewhere, so far as I know, doesPeganumgrow where the conditions are extreme, as might be concluded from the habit of the plant as given above.

[24]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.

[25]The Root Habits of Desert Plants,l. c.

[26]Compare the root-system of the species at Biskra, p.64.

[27]In the vicinity of Tucson (see The Root Habits of Desert Plants) is to be found a slender-stemmedOpuntiawhose 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. InCereus greggiithe subterranean 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.

[28]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 ofParietaria debilisgrowing 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 1. (Root Habits of Desert Plants,loc. cit.)

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

[30]Liste des plantes observées aux environs de Biskra et dans l’Aurés, Trabutet al., Alger, 1892.

[31]Briefly the case is as follows (see The root systems of desert plants,loc. cit.):Opuntia arbusculagrowing 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.

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

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

[34]Through Timbuctu and across the Great Sahara, 1912, p. 266.

[35]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 determined 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.

[36]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.

[37]Die Wasserversorgung und die osmotischen Druckverhältnisse der Wüstenpflanzen. Zeitschr. f. Botanik, 4, 1911.

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

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

Transcriber's note:pg15Added period after: vegetation of the countrypg17Changed:Quercus bollotato:ballotapg24Changed:Rhus oxycanthato:oxyacanthapg25Changed:Artistida pungensto:Aristidapg32Changed: Astericus pygmæus to: Asteriscuspg35Changed:Petama spherocarpato:Retama sphærocarpafootnote21(pg38) Changed: Statique to: Statistiquepg43Changed: were in in pre-M’Zabite to: were in pre-M’Zabitepg43Changed: iteslf to: itselfpg50Changed:Zillikoferiato:Zollikoferiapg53Changed: Fig. 441. to: 44.pg54Changed:Astericus graveolensto:Asteriscuspg55Changed:Tragonum nudatumto:Traganumpg56Changed:Phargmitesto:Phragmitespg57Changed: Maricandia cinerea to: Moricandiapg57Changed: Haloxylon articulata to: articulatumpg57Changed: Sorzonera nudulata to: Scorzonera undulatapg59Changed: P. albans to: albicanspg63Changed:Ferula visciritensisto:vesceritensispg65Changed:Ferula vesciritensisto:vesceritensispg73Changed: edaphacic to: edaphicOther spelling and formatting inconsistencies have been left unchanged

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