VEGETATION OF SOUTHERN NAMIB, 83 



Fairly common is Pteronia succitlenta, a dwarf shrublet with 

 mostly small, almost terete 1-^aves, that are usually only 3-5 mm. 

 long. . on luxuriant specimens only reaching" double the size. 

 Evidently the leaves, although persistent even in summer, are 

 well adapted to the extremes of the climate, for the fury of the 

 sand-laden wind has often forced the plant to crouch on the 

 ground or to seek shelter behind projecting rocks, isolated boulders 

 or even pebbles. Nowhere, not even on the stormy coasts of 

 the Cape of Good Hope, can the trimming effect of the wind be 

 seen to such an extent as here. Shrublets of Pteronia or Salsola 

 are not rarely trained into a narrow, sharp-edged wedge, ten 

 times as long as broad and closely pressed to the ground, the 

 mainstem being bent over at a right angle, immediately above 

 the projecting stone or pebble, behind which the plant had been 

 enabled to start its life. Where the shelter, however small it 

 might have been, has gone, the stem of the harder wooded plants, 

 as far as it projects above the ground, has been carved into a narrow 

 wedge with polished lateral faces, the sap evidently rising and 

 descending in the narrow strip of unexposed wood and bark 

 situated at the back. 



A leafless umbellifer. the widely spread Pitnranthiis aphyllns, 

 which, in the Karroo and other dry regions of South Africa, forms 

 upright bushes two to three feet high, has here assumed a crouching 

 habit, the stems growing almost horizontally in the direction 

 of the wind, viz. : south to north, retaining their upright growth, 

 only in sheltered places. 



Among the numerous species of Mesembriantheiniim occurring 

 in this region, are several of peculiar biological interest. One 

 of the most common kinds is M. fimhriatitm, of the section 

 Sphaeroidea, which forms little, rounded, grey lumps, attached 

 to the rocks, each branch! et being terminated by a corpusculum, 

 that is hidden among the remains of previous generations. 

 Another species of the same section is M. opticiim, one of the few 

 window-plants, described by me in another paper.* The plants 

 are nearly embedded in the ground, the apical part of the cor- 

 pusculum only being exposed to the air ; here no green tissue 

 exists, the end being transparent, thus allowing the light to enter 

 the body of the leaf and to illuminate the lateral green parts from 

 within. 



Belonging to another section, but possessing even more highly 

 specialised window-leaves, is M. rhopalophylliun, which is fairly 

 common in the coast belt from Angra Pequena to Pomona. The 

 plant is stemless and produces a large number of sessile, club- 

 shaped, erect leaves, about one inch long. The apex of the leaves 

 is convex, colourless and transparent like a lens, hence, as the 

 plant grows embedded in sandy or gravelly soil, nothing is seen 

 except these transparent spots, which peep out of the ground like 

 eyes. In spring the flowers appear, protruding about half an 

 inch above the ground, often the only indication of the existence 

 of the plant, as even the eyes may be covered with sand. 



* Trans. Roy. Soc. S.A., 1909. 



