46 BOTANICAL FEATURES OF THE ALGERIAN SAHARA. 



zontal course for 1.5 meters. It was 1.35 cm. in diameter at the crown and 

 2 mm. in diameter where left, at a depth approximating 27 cm. The main 

 root gave off a lateral 5.5 cm. from the surface of the ground, which also 

 branched; the ultimate branches followed a fairly level course for 45 cm. 

 At the sharp bend of the main root another branch arose and this branched 

 in turn, the daughter branches going somewhat downward for over 43 cm. 

 Branches from the latter roots descended to within 8 cm. of the surface. 



(See fig. 35.) 



Differing in details, the roots of other individuals of the same species in 

 the same habitat have on the whole a root-system essentially like the one 

 just sketched. Even in relatively or actually deep soil the roots of this 

 species do not penetrate deeply, but reach rather widely. They are of the 

 generalized type,* similar in many ways to the root-system of Covillea tri- 

 dentata of the Tucson region. When growing in a habitat where hardpan 

 comes close to the surface, the main root is not so well developed, but there 

 is a better development of laterals than in the specimen more favorably 

 situated as regards soil, in the habitat above alluded to. 



Growing in or near the habitat of Peganum harmala, whose root-system 

 has been sketched, were other species whose roots were also examined. 

 Among these were Haloxylon articulatum and Euphorbia guyoniana; the 

 former is one of the native plants most eagerly sought by animals for food, 

 for which reason it was not found possible to secure for study specimens 

 whose shoots were entirely normal; but the plants finally chosen were the 

 least damaged of any found outside of the protected areas. The shoot of 

 the specimen of Haloxylon examined was about 50 cm. high; its gnarled 

 base showed that it had been subject to intermittent attacks by animals. 

 It was found to have a main root which ran directly downward more than 

 30 cm.; at a depth of 10 to 15 cm. a few small laterals took their origin. 

 (Fig. 36.) The other specimens studied showed the same type of root- 

 system, so that Haloxylon has here a well-developed main root.f 



Growing not far from the two species whose root-systems have just been 

 sketched, and under similar soil conditions, were several specimens of 

 Euphorbia guyoniana, whose roots were also examined. This plant has a 

 habit of growing in groups whose members are more or less widely sepa- 

 rated. The first specimen studied was one of a colony of a half-dozen whose 

 habit of growth is shown in fig. 38. Its shoot was about 15 cm. high and 

 bore several narrow, smooth leaves, and was 2.5 mm. in diameter at the 

 base. The shoot was found to go directly downward until it joined a hori- 

 zontally placed fleshy root, from which the other individuals of the colony 

 were seen to take their origin. This, apparently a root-stock, was 8 mm. in 

 diameter and gave off two branches, 3 and 5 mm. in cross-section, which 

 were also horizontally placed. 



* The Root Habits of Desert Plants, I. c. 



t Compare the root-system of the species at Biskra, p. 64. 



