44 BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 



The cemetery situated wholly on the edge of the plain has an unexpect- 

 edly large number of plants, almost all of them Haloxylon articulatum, 

 which is of good size. Outside this protected area the species is neither 

 large nor abundant, since it is eagerly sought after by camels, sheep, and 

 goats, and a shoot no sooner appears than it is eaten to the base. 



The sentiments of the residents of Ghardaia, which led to the establish- 

 ment and protection of the cemeteries, made a close botanical study of 

 them injudicious. Enough was seen, however, to establish several points, 

 the most important being, at least for the areas considered, that there is 

 growing in them, without irrigation, a somewhat rich flora composed of 

 relatively large perennials. And from this fact it seems probable, if also 

 protected against the predatory attacks of animals, that other areas under 

 the present rainfall and other physical environmental conditions now 

 obtaining would support a much heavier vegetation than is generally the 

 case. How far the presence of man and of his flocks has otherwise modi- 

 fied the flora, especially as regards its composition, is another question, 

 but it certainly has not been without its effect. In the portions of the 

 M'Zab region, except certain areas rather remote from the towns, where 

 there is no protection, the only forms which are at all abundant, or at least 

 conspicuous, are such as are armed, poisonous or distasteful, or too small 

 for use as fuel. Among these are Peganum harmala, Zilla macroptera, Tam- 

 arix, and others seen later. However, Haloxylon articulatum, although 

 eaten by all animals so as never to develop in a normal manner, is surpris- 

 ingly abundant, although by no means conspicuous. 



ROOT-HABITS IN THE GHARDAIA REGION. 



Owing to the small amount of soil, close observation of the root-systems 

 of the plants growing on the mountains and the plain was difficult ; exami- 

 nation of the roots in the field was therefore carried on mostly in the valley, 

 although enough was seen of the roots of plants in the other habitats to 

 permit a characterization of them. The roots of several species growing on 

 the hamada close to the valley were examined with the following as the 

 leading results: Deverra scoparia was found to have a main root running 

 directly downward 20 cm. without giving off large laterals; at that depth 

 it forked, the resultant branches running thereafter in a horizontal direc- 

 tion. (See fig. 33.) Teucriumpseudo-chamcepitys, Centaureapubescens, and 

 Salvia eegy plica, all from the hamada to the north of the M'Zab Valley, 

 have pronounced main roots. A similar type of root was seen in Zolli- 

 koferia resedifolia and Fagonia bruguieri from the plain to the south of 

 the valley. Grasses growing on the plain had roots which, as usual with 

 grasses, showed more diversity, but on the whole penetrated rather deeply. 

 The root-system of Haloxylon articulatum is of the modified generalized 

 type, penetrating deeply also, and will be best described as an inhabitant 

 of the valley. 



