320 OUTLINE OF PLANT GEOGRAPHY 



Africana, and a poisonous plant, Dichapetalum toxicarium belong- 

 ing to the predominantly African family Dichapetalaceae. 



West of Transvaal and Rhodesia the precipitation falls off, 

 and along the Atlantic coast true desert conditions prevail. The 

 bush-veldt gives place to open formations with a fairly extensive 

 vegetation in the less arid portions, but over much of the region 

 the vegetation is extremely scanty. This great arid region is the 

 Kalahari Desert, and occupies most of the table land west of the 

 Transvaal and Rhodesia. The whole region has a scanty rainfall, 

 in some places an annual precipitation of only about four inches. 



At the extreme north there are a good many species of tropical 

 origin, but on the whole the species are the same as those of the 

 adjacent regions, and there are few peculiar to the Kalahari. 

 The grasses are thin and scattered, and there are scrubby bushes 

 and stunted trees in many places, the commonest being the wide- 

 spread Acacia giraffae. 



Among the herbaceous plants of the Kalahari are several of the 

 melon family, including, according to Engler, true water melons 

 (Citrullus vulgaris), which are highly prized by man and beast. 



Travelling southward from the Orange State one descends from 

 the high table land toward the lower arid region of the Karroo. 

 This has a very dry climate, sometimes almost rainless for periods 

 of a year or more. When, however, the rains come, there is a 

 surprising amount of vegetation developed, many species having 

 underground tubers or bulbs which may remain dormant indefi- 

 nitely, only waiting for sufficient moisture to put forth leaves and 

 flowers. Shrubs and trees quickly unfold fresh green leaves which 

 are destined soon to wither away. 



Trees are scarce, but there are many low shrubs scattered over 

 the landscape, which is not unlike that of parts of Nevada or Ari- 

 zona. As in the southern American deserts, there is a marked 

 development of succulents, but the place of the American Cacti 

 and Agaves is taken by cactus-like Euphorbias and Aloes. In 

 some places, however, true Cacti (Opuntia spp.) may be seen, but 

 these prickly-pears, although completely naturalized, are escapes 

 from cultivation. 



As in the Cape region, there are many showy species of Mesem- 

 bryanthemum, and the curious Stapelias, members of the milk- 

 weed family are characteristic of the Karroo. The latter have 



