26. Upper surface of rocks, showing small incrusting
lichens, on a low mountain about 5 km. north
of M’Zab Valley, Ghardaia.
Pl. 11, fig. 27. Habitat of _Peganum harmala_, at Melika, Ghardaia.
28. Shoot and leaf habit of _Peganum harmala_, from
Ghardaia.
Pl. 12, fig. 29. Habit of _Henophyton deserti_ at Ghardaia when
growing in a protected situation (cemetery).