PLANT SUCCESSION. 237 



IV. Bases of Colonisation. 



The main base of colonisation for the greater part of the area 

 under study is the shallow "central valley." This is about 800 

 yards long from the head to the railway line which forms the lower 

 boundary of the area investigated. Near the head is a spring 

 from which a small stream of water flows through the valley. The 

 western side is somewhat steeper than the eastern, which is broken 

 by two 1 or three depressions, tributary to the valley itself. The 

 valley is well stocked with trees, of which the following is an 

 almost complete list : — 



Combretum kraussii, Ficus capensis, Cussonia spicata, Zizy- 

 phus mucronata, Moesa rufesceus, Clerodendron glabrum, Fagara 

 capensis, Gymnosporia buxifolia, Erythroxylon monogynum, 

 Royena pattens, Dombeya rotundifoUa, Halleria lucida. 



The trees are named roughly in the order of their abundance 

 in the valley. They occur principally on the sides of the valley 

 and not close down to the stream, though Moesa rufescens is most 

 plentiful near the spring at the head of the valley. The trees 

 tend to grow in clumps, which become larger and denser as one 

 proceeds up the valley. In each clump one can usually find the 

 oldest tree in the centre, generally one of the first three in' the 

 above list, surrounded by a number of younger trees. Straggling 

 over the clumps are numerous climbers such as Asparagus sp., 

 Rhoicissus cirrhiflora, Rubus pinnatus } Clematis brachiata, 

 Smodingium argutum, Mikania scandens (?). Plectronia spinosa 

 is common in all the clumps, growing in the spaces between the 

 trees. 



As will be seen from the list given above, the two commonest 

 trees are Combretum kraussii and Ficus capensis. Of these the 

 latter is found principally towards the head of the valley, and 

 usually well up on the sides. The former is commoner lower down 

 and grows nearer the stream. 



Numerous shrubs and herbs occur, growing either in the open 

 or round the edges of the clumps. The following is a list of those 

 in flower at the present time (July, 1921): — 



Teucrium africanum, Phytolacca sp., Lantana camara, 

 Solanum nigrum, Berkheya sp., Buddleia salviaefolia, Leonotis 



leonurus, Artemisia afra, and one or two Acanthaceae. 



A second base of colonisation is the eastern valley (valley 

 "B"), which is rather deeper than the one just described. It is 

 also traversed by a stream of water, which has cut a deep, narrow 

 channel through the bed of the valley. The vegetation in this 

 valley resembles that in the one just described, except that the 

 trees grow much closer to the stream and do not form clumps 

 except higher up on the sides of the valley. This valley contains 

 in addition to the trees listed for the "central valley" Acacia 

 horrid a and a few others. 



