Part 19

Illustration: Fig. 36. Root-systems of Helianthemum sessiliflorum (right), Haloxylon articulatum, and Nolletia chrysocomoides (left), from the flood-plain of the Oued M’Zab, Ghardaia.]

Illustration: Fig. 37. Shoot and root habit of Citrullus colocynthis. Oued M’Zab, Ghardaia.

Illustration: Fig. 38. Euphorbia guyoniana, in the valley of the Oued M’Zab at Ghardaia.]

Illustration: Fig. 39. Habit of Euphorbia guyoniana. Ghardaia.

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

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

Illustration: 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.]

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

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

Illustration: 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.]

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

Illustration: 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.

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

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

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

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

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

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

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

Illustration: Fig. 55. Shallow well about 25km. north of Ouargla.]

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

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

Illustration: 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.

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

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

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

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

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