FLORISTIC REGIONS 103 



SAHARAN REGION. The greatest desert in the world, 

 the Saharan Region, represented, as we have seen, in the 

 Canary Islands, extends across Africa, between the 

 parallels of 20 and 35 N., Arabia, Southern Persia, and 

 Baluchistan to Sind. It is exposed to the unchecked 

 prevalence of the north-east trade-wind, and its inco- 

 herent soil, stony or sandy, is often blown into dunes. 

 Sparse and stunted as is its vegetation, plants are not 

 absent. Where scanty spring rain occurs, shallow- 

 rooted annual species of Malcomia, Rcemeria, and 

 Astragalus spring up, with the Rose of Jericho (Anasta- 

 tica hierochuntica L.) and the water-storing Ice-plant 

 (Mesembryanthemum crystallinum L.), a member of the 

 characteristically desert family the Aizoacece. Some of 

 these, though apparently hygrophilous, are only enabled 

 to survive by the enormous distance to which their roots 

 spread horizontally. Such, for instance, is the case with 

 the annual gourd Citrullus Colocynthis Schrad. Other 

 plants are more obviously xerophytic, being mostly very 

 deep-rooted shrubs dependent upon those subterranean 

 waters which rise to the surface in the springs of the 

 oases, the home of the Date-palm (Phcenix dactylifera 

 L.). Among these are spinous Acacias, such as A. Seyal 

 Del.; Alhagi, the Camel-thorn; Zygophyllacece, such as 

 Nitraria, Zizyphus Spina-Christi Willd. ; the broom-like 

 Genista R&tam Forsk. ; Capparis spinosa, coated with 

 wax; A triplex Halimus L., covered with vesicular hairs; 

 cactus-like Euphorbias; erect shrubby and prostrate 

 species of Convolvulus ; Grasses with inr oiled leaves, 

 such as Cynodon Dactylon Pers. ; bulbous species of 

 Ornithogalum, Allium, Urginea, etc. ; the fleshy Stapelias, 

 with their evil-smelling fly-haunted blossoms; and 

 many species with fragrant ethereal oils, balsams, gum- 

 resins, and exudations of gum. Such are the species of 

 Ferula, the gum Acacias, and the incense-yielding 

 Boswellia and Balsamodendron, which gave to the south- 

 ward extension of this region into Somaliland and 

 Southern Arabia the name of the " Region of Balsamic 

 Trees." 



CENTRAL ASIAN DESERT. This desert is almost con- 

 tinuous, through that of Syria and Mesopotamia, with 

 the great Central Asian desert, which is entirely extra- 

 tropical and has an extreme climate. It consists of the 

 plains between the Caspian and the Thian-Shan Moun- 



