Leaf-Habits in the Ghardaia Region 49 Growth and Flowering Habits in the Ghardaia Region 49 Ghardaia to Touggourt 50 Ghardaia to Ouargla—Vegetation 53 Ouargla to Touggourt—Vegetation 56 Touggourt to Biskra—Physical Features and Vegetation 58 The Biskra Region 59 Topography 59 Plant Habitats of the Biskra Region 60 Vegetation of the Biskra Region 61 General Summary and Conclusions 66 The Environmental Conditions of Plants in Arid Regions 66 Environmental Features of the Flora of Algeria 69 Some Effects of Temperature and Rainfall in Southern Algeria 71 The Soil Relation in Southern Algeria 73 Root-Characters and Species Distribution in Southern Algeria 76 The Biotic Factor 77 Comparison of Some General Features of the Vegetation of Southern Algeria and of Southern Arizona 79 LIST OF ILLUSTRATIONS. * * * * * Plate A. Outline map of Algeria, showing main features of surface drainage. Pl. 1, fig. 1. View of the oasis of Laghouat. 2. Wood market at Laghouat. Juniper, oak, pine, and other kinds of wood, each bunch a camel load, exposed for sale. 3. Wood market at Laghouat. Roots of _Zizyphus_, branches of juniper and pine, and pine bark. The latter is said to be used for staining. Pl. 2, fig. 4. Shoot-habit of _Acanthyllis tragacanthoides_. Laghouat. 5. Shoot-habit of _Zollikoferia spinosa_. Laghouat. 6. _Acanthyllis tragacanthoides_ on sandy plain. Laghouat. 7. _Zollikoferia spinosa_ in habitat, plain (hamada). Laghouat. Pl. 3, fig. 8. Detail of north slope of Nomad Mountains, where _Zollikoferia spinosa_ is the dominant species. Laghouat. 9. Vegetation of plain (hamada) at Tilrempt. The conspicuous shrub is _Haloxylon articulatum_. 10. The daya of Tilrempt from the plain, showing the character of the depression.