34. Root-habit of _Gymnocarpos fruticosum_, from plain about 3 km. north of M’Zab Valley at Ghardaia. Pl. 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 comparatively deep. Pl. 15, fig. 36. Root-systems of _Helianthemum sessiliflorum_ (right), _Haloxylon articulatum_, and _Nolletia chrysocomoides_ (left), from the flood-plain of the Oued M’Zab, Ghardaia. Pl. 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. Pl. 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-chamæpitys_. From Ghardaia. Pl. 18, fig. 41. Habit of _Salsola_ sp. (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_. Pl. 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 without plant life. Pl. 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. Pl. 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. Pl. 22, fig. 51. Vegetation, mainly _Ephedra_ and _Retama_, of the western edge of the Chott Mellala.