42 BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 



tributed plants in the valley are Peganum harmala (figs. 27 and 28) and 

 Haloxylon articulatum; the former is a half-shrub of wide distribution in 

 southern Algeria, occurring from Biskra on the north, and although not 

 strictly confined to the flood-plains of the oued is most abundant where 

 the soil is relatively deep. The leaves are rather large and do not appear to 

 have unusual protection against drought.* Like its relative in the south- 

 western portion of the United States, the creosote bush (Covillea tridentata), 

 it is not eaten by any animals, although not armed and not poisonous. This 

 species, therefore, is one of the few which to-day probably retains essen- 

 tially the same distribution and appearance it had before the country was 

 inhabited. It is interesting to note that Peganum is generally distributed 

 through the M'Zab Valley, being especially abundant between Ben Isguen 

 and Melika. Here in November Peganum, except where trodden under 

 foot by the flocks and caravans, retained much of its foliage, although rain 

 was said not to have fallen for twelve months. In the protected areas also, 

 as will be mentioned below, this species was found to be fresh green, show- 

 ing little or no indication of the long drought. Of other species found in 

 unprotected places in the valley, Haloxylon articulatum and Henophyton 

 deserti, although eaten by animals so as to be recognized only with difficulty, 

 were also fairly abundant. There were found also Euphorbia guyoniana, 

 called "le bain" by our French-speaking Arab helper, because it is used by 

 the natives as a soap, and Nolletia chrysocomoides, Mluropus sp., and others. 



PROTECTED AREAS NEAR GHARDAIA. 



Of the plant habitats whose leading characteristics have been briefly 

 given above, only the oasis and its gardens are secure against the inroads 

 of animals. However, owing to the long settlement of the region, rather 

 large tracts of land are at present in what must nearly approach their 

 primitive condition. The areas referred to are the cemeteries, which, for 

 the reason suggested, possess special interest to the botanist, showing 

 briefly what plants might be expected to occur in the region naturally. 

 The typical M'Zab cemetery is of varying size and surrounded by a stone 

 wall. No plants are introduced to decorate it and no irrigation is practised 

 within its walls. The only disturbance of the natural condition of the land 

 is in the use for which it is set aside. The interments are so conducted 

 that the ground appears to be always used progressively, that is, there is 



* Fitting (Die Wasserversorgung und die osmotischen Druckverhaltnisse der Wiisten- 

 pflanzen, Zeitschr. f. Bot., 4, 209-275, 191 1) states that water-storage tissue is wanting, 

 that in addition to being large, the leaves are much divided, without trichomes, and 

 provided with thin cuticle. The stomata are fairly large, rather numerous, and not 

 sunk. The leaves transpire rapidly and wilt socn after being removed from the stem. 

 The osmotic pressure of the cell-sap of the leaves was found to equai 35.3 to 64 atmos- 

 pheres, from which it is assumed that this plant, like others growing under desertic 

 conditions, has a root cell-sap of great osmotic pressure, which permits it to extract 

 water from a fairly dry soil or at a rather rapid rate. But neither at Biskra nor else- 

 where, so far as I know, does Peganum grow where the conditions are extreme, as might 

 be concluded from the habit of the plant as given above. 



