135 



Setarias, Erianihus, Leersia, Paniciim criis-pavonis, Phalaris 

 arundinacea, Arundinella, Eragrostis nebvlosa, etc., and most 

 important of all the Tamibookie associes, A. nardus var. 

 validus, A. auctus, A. dregeanus. 



As the donga deepens and extends backwards from the 

 upper end, the sides fall in and the soil gets washed away. 

 The grasses then are confined to the sides and the mid-channel 

 is left bare. Birds and other animals seek shade and shelter 

 in the dongas and bring a great variety of seeds. Shrubs and 

 trees, if these are present in the neighbourhood, are brought 

 in in considerable variety and soon the donga vegetation 

 becomes very mixed indeed. As the shrubs and young trees 

 grow up only the shade-loving grasses, e.g., species of Pani- 

 cum, Stifa, etc., are able to persist. The climax stage, which, 

 however, is not a very stable climax, is Rocky Stream-bank 

 Bush with such species as Rauicolfia natalend,<i, Combretum 

 kraussli, C. salicifolium, Ficus capensis, F. natalensis, 

 Rhamnus prinoides, Celtis hrmissiana, Trerna hracteolata, 

 Grewia lasiocarpa, G. occidentalis, G. caffra, Buddleia salviae- 

 folia, Brachylaena discolor, Cussonia spicata, Calodendron 

 capense, Nuxia floribwtda, Xymalos monospora, Helinus 

 ovata, Celastrus buxifolms, Hippobromiis alata, Ehretia hot- 

 tentottica, Jasminum spp., Zizyphus imtcronata, Acacia spp., 

 Royena spp, Pavetta spp., Randia rudis, Xanthoxylon 

 capense, Euclea spp, Elaeodendron spp, and at higher altitudes 

 Leucosidea sericea. 



Dongas may be caused to silt up by placing an obstruc- 

 tion at the lower end, and sometimes natural obstructions 

 occur through fallen trees, etc. Above all, the earlier grass 

 stages in a donga succession should never be burnt, since they 

 do much to bind the soil and check the process of erosion. 



THE COAST BELT AND COAST LINE OF NATAL. 



The Psammoseke. Litoeal Species. The whole coast line 

 along the Eastern side of South Africa is low-lying without 

 any extensive development of cliffs. The line of sand dunes, 

 which varies from 50 to 200 feet in height and from a quarter 

 of a mile to half a mile in width, is clothed for the most 

 part with Psammophilous Bush, which represents the climax 

 stage of the succession. The only interruptions are the. Man- 

 grove associations at the river-mouths. The plant succession 

 on the strand, i.e., on the shifting belt of sand between the 

 fixed dunes and the sea, is a very clearly defined one. At 



