52. Approach to western edge of the Chott Mellala, showing characteristic rounded hills, or mamelons. Pl. 23, fig. 53. View between the Ouargla plain and the Chott Mellala, showing characteristic appearance of eroded hills. 54. Looking toward the Ouargla plain (reg). 55. Shallow well about 25 km. north of Ouargla. Pl. 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. Pl. 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. Pl. 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. Pl. 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. Pl. 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. Pl. 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. Pl. 30, fig. 68. Flood-plain of the Oued Hamman es Salahin, Biskra. Halophytes of various species occupy the foreground. 69. Habitat of _Phelyæa violacea_ shown in figure 70. Pl. 31, fig. 70. Young shoots of _Phelypæa violacea_, at north base of Ed Delouatt hills, Biskra. 71. Habit of young specimens of _Phelypæa_. Except for about 15 cm., plants were buried by sand. Biskra. Pl. 31, fig. 72. _Asphodelus_ sp. at north base of Ed Delouatt hills, Biskra. Photographed in March.