Chap. IX] 



DESERTS 



629 



shrubs (Terminalia prunioides), and a liane, Clematis orientalis, subsp. 

 brachiata. 



The character of the vegetation from the sea-shore up to the borders of 

 the semi-desert steppe and woodland of Kalahari undergoes a gradual 

 transformation in successive belts. This is partly due to the differences 

 in the physical nature and humidity of the soil, partly to differences in 

 climate. At a few miles' distance from the shore with its stunted halophytic 

 flora there is a broad belt of dunes and rocks, on which, at isolated spots, 

 nestle little colonies of a Gie- 

 seckia, of a Zygophyllum, or of 

 Aristida subacaulis ; they are of 

 short duration, for they are soon 

 buried under the sand that is 

 brought thither by the wind. 

 Only one plant there can with- 

 stand the force of the wind, 

 Ectadium virgatum, var. lati- 

 folium, a shrubby asclepiad 

 reaching a meter and a half high, 

 with rod- like branches and thick 

 leathery leaves. This does not 

 however grow in the sand, but 

 is rooted between rocks and 

 confined to their lee side. 



Beyond the dunes the vege- 

 tation becomes somewhat richer 

 with the appearance of subterra- 

 nean water. The melkbosch, a 

 succulent species of Euphorbia 

 (Fig. 360), appears ; ' like hay- 

 cocks on an immense meadow, 

 these dark grey bushes, one and 

 a half to two and a half meters 

 in height, stand scattered over 

 the white sandy tract 1 .' The 

 Euphorbia is always accom- 

 panied by the large root-parasite Hydnora africana. Still further eastwards, 

 other shrubs gradually appear — stunted Byttneriaceae, Acanthaceae, and 

 Scrophulariaceae. They gradually become more numerous, and finally the 

 first tree, Aloe dichotoma (Fig. 361), is met with. The desert character 

 becomes less marked ; the low acacia-woodland (Fig. 364), the dry 

 Aristida-steppe of the Kalahari, commences. 



1 Schinz, I. 



Fig. 362. Flora of the South-west African desert. 

 Pelargonium undulatum, Soland. A tuberous plant 

 of the Cape-flora. One-half natural size. After 

 Andrews. 



