5-— SOME OBSERVATIONS IN THE WELWITSCHIA 

 DESERT. * 



By H. H. W. Pearson, M.A., Sc.D., F.L.S. 



[Abstract.] 



Welwitschia is confined to the littoral srrip of desert which, 

 commencing near the mouth of the Orange River, extends north- 

 wards far into the Tropics. The observations recorded were made 

 in January and February, 1907, in the neighbourhood of Haikam- 

 chab and Welwitsch, situated in the most southern area from which 

 the plant is known.! 



The Flora of the desert belt (the " Namib ") is of a marked 

 desert type, and is mainly characterised by several highly peculiar 

 and endemic forms. The western fringe of the Namib is occupied 

 by sand-dunes, many of \vhich are as much as 200 ft. high. Their 

 vegetation is very scanty, and it appears that the whole phanero- 

 gamic flora of the dunes of Walfish Bay comprises no more than a 

 dozen species. Of these, two are of special interest, viz. Acaritho- 

 sicyos horrida and Tamaria articulata. The former, a member of 

 the Cucurbitaceae, is well adapted to growth in accumulations of 

 sand, and many of the large dunes owe their stability and, indeed, 

 their existence to this plant, whose deep roots serve as anchors. 



East of the sand-dunes, where the surface is hard, the flora is 

 richer in species, though in many localities considerable areas are 

 quite destitute of flowering plants. The vegetation consists chiefly 

 of deep-rooted woody perennials of low habit, and with small 

 leaves. Among these are Zygo-phyllum Staffii — a very character- 

 istic Namib plant, and one of the surprisingly few succulents met 

 with. Commiphora saxicola, Sarcocaulon sf. — whose stems are en- 

 cased in an armour of hard wax, a Bauhinia, a few Capparidaceae, 

 and Blepharids. The grasses are rather numerously represented in 

 sandv places bv species of Aristida and prostrate Cucurbitaceae are 

 not infrequent. The arborescent Aloe dichotoma is common among 

 the barren crags of the broken country overlooking the main river- 

 beds. 



Welwitschia occurs abundantly on the Namib plateau, and 

 descends the ravines leading down to the deeper river-channels. Its 

 altitudinal range is about 400 ft. Pollination is mainlv, if not 

 entirely, effected by the hemipteron, Odontofus sexfnnctnlatus, as 

 has already been described (Nature, Vol. 75, pp. ^^fi, 53?)- Sub- 

 foliar inflorescences commonly occur. 



Fertilisation rarelv fails and very large numbers of fertile seeds 

 are produced. No germinating seeds, nor young seedlings, were 

 found, and it appears 4:hat the conditions necessary for effective 

 reproduction rarelv occur. 



The Namib flora must be regarded as of great age, and it must 

 be supposed that the climatic conditions at present prevailing in 



* Assisted by a grant from the British Association. 



t I was accompanied on th^s expedition by Mr. E. E. Galpin, F.L.S. 



