Illustration: 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 States.] [Plate 7: Illustration: Fig. 18. Shoot-habit of Haloxylon articulatum, from the plain near the Daya of Tilrempt. Illustration: Fig. 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).] [Plate 8: Illustration: Fig. 20. Vegetation in upper part of a “draw” on plain north of the M’Zab Valley Ghardaia. Illustration: Fig. 21. Situation of square No. 2. on plain north of valley at Ghardaia.] [Plate 9: Illustration: Fig. 22. Capparis spinosa at base of valley wall at Ghardaia. Illustration: Fig. 23. Leaves of Capparis spinosa, from Ghardaia.] [Plate 10: Illustration: Fig. 24. Leaf-habit of Dæmia cordata. Ghardaia. Illustration: Fig. 25. Shoot-habit of Salvia ægyptica. Ghardaia. Illustration: Fig. 26. Upper surface of rocks, showing small incrusting lichens, on a low mountain about 5km. north of the M’Zab Valley, Ghardaia.] [Plate 11: Illustration: Fig. 27. Habitat of Peganum harmala, at Melika, Ghardaia. Illustration: Fig. 28. Shoot and leaf habit of Peganum harmala, from Ghardaia.] [Plate 12: Illustration: Fig. 29. Habit of Henophyton deserti at Ghardaia when growing in a protected situation (cemetery). Illustration: Fig. 30. Leaf-habit of Henophyton deserti. Ghardaia.] [Plate 13: Illustration: Fig. 31. View in a cemetery at Ghardaia, to show the relatively abundant vegetation. Illustration: Fig. 32. View in an M’Zabite cemetery, Ghardaia. Haloxylon articulatum is the leading species shown.] [Plate 14: Illustration: Fig. 33. Habit of Deverra scoparia, from plain about 3km. north of M’Zab Valley, Ghardaia. Illustration: Fig. 34. Root-habit of Gymnocarpos fruticosum, from plain about 3km. north of M’Zab Valley, Ghardaia.] [Plate 15: Illustration: 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. (See text for further explanation.) 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.] [Plate 16: 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.] [Plate 17: 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.] [Plate 18: Illustration: Fig. 41. Habit of Salsola sp. (below), and Echinopsilon muricatus, from the M’Zab Valley, Ghardaia.