CHAP. Lxxiii SHRUB-STEPPE 279 



abundant is the ' everlasting sage-bush ', Artemisia tridentata, an under- 

 shrub that extends over areas so vast that the eye can see nothing beyond : 

 yet it never grows so densely as to bar the way. Usually it does not 

 exceed i metre in height. Mingled with this species, on the frequently 

 salt soil, are Atriplex confertifoha, A. canescens, Artemisia spinescens, 

 Kochia prostrata, Eurotia lanata, Grayia polygaloides, and others.^ 



Composita-steppe in Cape Colony. 



The summits of the table mountains of Cape Colony north of the 

 Karroos are clothed with steppe-vegetation in which undcrshrubs pre- 

 dominate and mainly belong to the Compositae. The most important 

 genera are Helichrysum, Senecio, Berkhaya, Euryops, Pentzia, and 

 (jazania. Common also are Leguminosae, Crassulaceae, and Scrophu- 

 lariaceae. Bulbous and tuberous plants are represented by very numerous 

 species.- In Asiatic and North-American steppes Compositae are in like 

 manner dominant in certain places. 



Succulent Steppe. 



Within the cold-temperate zone succulent plants occur in considerable 

 numbers only on soil saturated with salts ; whereas in the subtropical 

 zone succulent shrubs and undershrubs, as well as succulent perennial 

 herbs, form an important part of the vegetation. In the Old World it is 

 species of Euphorbia that come to the fore, but in the New World, 

 Cactaceae. 



North Africa. In Morocco there is bushland composed of species of 

 Euphorbia. The leading species, Euphorbia mauritanica, bears foUage 

 during winter, but is leafless in summer. 



The lower-lying land of the Canary Islands is mountainous country 

 traversed by deep clefts whose slopes are occupied by a characteristic 

 steppe-vegetation. The largest shrubs belong to the cactus-like Euphorbia 

 canariensis, and to Kleinia neriifolia and Plocama pendula, all of which 

 are succulents. Among shorter shrubs, which are usually about i metre 

 in height, are several species of Euphorbia. Of these E. aphylla is 

 aphyllous, but the others are leafless only in summer. Intermingled with 

 the shrubs are xerophytic undershrubs, and above an altitude of 100 

 metres these are accompanied by great numbers of Crassulaceae, together 

 with grasses that possess rolled leaves, bulbous plants (including Urginea 

 and Scilla), and annual herbs.^ The highland of Cape Verde Isles is 

 likewise Euphorbia-steppe. 



North America. The rocky, dry plateaux of Texas and Mexico must 

 also be regarded as belonging to the same general type. But here are 

 found species absent from the Old World, including those of Agave, 

 Yucca, and, above all, Cactaceae. Cereus giganteus, the Mexican giant- 

 cactus, raises its mighty candelabra-like branches up to a height of 

 18 metres, and covers the hills to such an extent that at a distance these 

 seem to bristle with needles. Other Cactaceae produce short, richly 

 branched stems that are beset with white spines ; and yet others creep 



' Pound and Clements, 1898- 1900. ^ Bolus, 1886. 



" Christ, 1885 ; Vahl, 1004^; Schroter, 1908. 



