129 



Acacia thorn trees, germinate among the Anthistiria-Andro- 

 pogon grasses. They grow up and form a park-like type ci 

 vegetation. Birds alight on their branches, and bring the 

 seeds of numerous other species, which are deposited under- 

 neath the pioneer trees, and grow up in their shade. Clumps 

 of trees are thus formed, and as the clumps grow closer Thorn 

 thickets are established. The climax type is Scrub. For full 

 details see S.A. Journal of Science, November, 1917, where a 

 list of over 23U species of Thorn Veld trees and shrubs is 

 given, with an account of their relative frequency and 

 behaviour in the plant succession. 



The Hydrosere. 



The initial stages develop along the margins of Vleis and 

 ponds, and along the stream banks, and consist of hygro- 

 philous consocies. The variations (1) in the amount of water 

 present and (2) in the degree of stagnation of the water deter- 

 mine the different types. In the larger Yleis, different stages 

 of succession are marked by a more or less perfect zonation, 

 the earlier stages being nearest the centre of the Vlei and the 

 later transitional stages being on the side nearest to the Veld 

 grassland. In the smaller Vleis and along the stream banks, 

 only a few of the stages are represented at any one spot. 



The first stage consists of floating or submerged aquatic 

 plants of which two types may be distinguished: — 



(1) In well aerated, running water, Mosses and Hepatics 

 with a few well developed Algal communities, and such plants 

 as Hydrostachys natalensis, Triglochin Icutiflorum, T. 

 striatum, Eriocaulon tvoodii. 



(2) Less well aerated standing water. Algae more 

 numerous, Mosses and Hepatics less abundant, and more 

 numerous aquatics, e.g., Marsilea macrocarpa, Lemna minor, 

 L. gibba, CallitricJie bolusii, Limn anthe mum indicum, 

 Myriophyllum spicatum, Pistitt stratiotes, Nympliaea stellata, 

 N. capensis, Ceratophyllum sp., Aponogeton natalense, and 

 several species of Utricularia and Potamogeton. 



The second stage is represented by various zones of tall 

 Cyperaceae and Phragmites communis with Typha capensis. 

 Phragmites lines many of the streams for long distances and 

 Typha forms very definite consocies or occurs mixed with the 

 Phragmites and sedges. Cyperus immensns is the tallest of 

 the sedges, but C. latifolius is the commonest. Cyperus 

 fastigiatus is also common, and there are a great many others 



