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.
Pl. 4, fig. 11. Near view of the daya of Tilrempt. The fortified
stage station, bordj, and a nomad camp are to
be seen. The flattened, level, lower surface of
the trees is the effect of grazing, mainly by
camels.
12. Jujube (_Zizyphus_) shrubs and betoum
(_Pistacia_) at the daya of Tilrempt.
Pl. 5, fig. 13. A young specimen of betoum in the midst of a
protecting jujube at the daya of Tilrempt.
14. Leaf and shoot habit of the jujube (_Zizyphus
lotus_). Daya of Tilrempt.
15. Leaves of the betoum (_Pistacia atlantica_) from
the daya of Tilrempt.
Pl. 6, fig. 16. South wall of the valley of the Oued M’Zab at
Ghardaia.
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.
Pl. 7, fig. 18. Shoot-habit of _Haloxylon articulatum_, from the
plain near the daya of Tilrempt.
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).
Pl. 8, fig. 20. Vegetation in upper part of a “draw” on plain
north of the M’Zab Valley, Ghardaia.
21. Situation of square No. 2, on plain north of
valley at Ghardaia.
Pl. 9, fig. 22. _Capparis spinosa_ at base of valley wall at
Ghardaia.