Chap. IX] 



DESERTS 



631 



many of the Karroo plants are thorny and are thus somewhat protected 

 against the roaming herds of antelopes. 



The most remarkable plants of the South African desert are Welwitschia 

 mirabilis (Fig. 367) and the cucurbitaceous Acanthosicyos horrida, both of 

 which are confined to the northern part of the littoral district, from Walfish 

 Bay to Cape Negro, and occupy only isolated spots within their areas 

 of distribution : — 



Fig. 367. Flora of the South-west African desert. Welwitschia mirabilis. One-sixth 



natural size. 



Welwitschia mirabilis, belonging to the Gnetaceae, was first discovered in i860 by 

 Welwitsch at Mossamedes, but is also abundant more to the south near Walfish 

 Bay : it inhabits the stony tracts in the littoral district (Fig. 363). It consists 

 of a short, almost tuberous, unbranched stem, which projects only a decimeter 

 above the ground and tapers downwards into a long tap-root. The part of the stem 

 above the ground, which attains a girth of four meters and is invested with reddish 

 bark, exhibits a saucer-like depression at its two-lobed apex, on the margin of 

 which arc two extremely long, opposite, riband-like leaves, the sole assimilatory 



