240 PLANT SUCCESSION. 



stage in the succession is the arrival of Acacia ataxacantha, which 

 straggles over the whole clump, killing out many of the earlier 

 arrivals, and forming a dense, almost impenetrable thicket. 



VII. The Mature Clumps — Detailed Analysis. 

 The fully formed clumps all closely resemble one another, 

 though showing slight variations in their composition. In the 

 centre of each there is usually a large Cussonia spicata, at the 

 base of which is a termites' nest. It would be interesting to know 

 whether this nest is formed before or after the arrival of the 

 Cussonia. In his account of the thorn veld (4) Professor Bew3 

 states that "seeds of all the species are apt to be distributed and 

 to germinate on or around white ants' nests." In the one case 

 already mentioned of the earliest observed stage of the succession 

 there was no termites' nest present, but the young Cussonia was 

 growing on an ordinary ants' nest. An isolated case like this, 

 however, does not afford sufficient evidence on which to base any 

 definite conclusions. The Cussonia in the centre of the clump is 

 frequently dead, and in many cases only the stump is left, the 

 tree itself having fallen. The cause of the death of this tree is 

 believed to be the attack of white ants, but this subject is reserved 

 for discussion in a later section of the paper. 



Surrounding the central tree is a ring of younger trees, the 

 commonest of these being Conibretum kraussii and Glerodendron 

 glabrum. A bare space is usually left in the centre of the clump 

 round about the Cussonia. Between the trees forming the outer 

 ring there is usually a plentiful growth of Plectronia spinosa and 

 other Rubiaceae. Scrambling over the trees are various climbers 

 such as Rubus pinnatus, Smodingium argutum, Rhoicissus cirrhi- 

 flora, Helinus avatus, Mikania scandens (?), and Asparagus sp. 

 Numerous herbs occur round the edges of the clumps, e.g., 

 Teucrhim africanum, Lantana camara, and various Acanthaceae. 

 Many others probably occur, but do not flower until later in the 

 year, and consequently were not noted. 



The following detailed notes on several typical clumps will 

 illustrate the variations which occur. Since the climbers, shrubs 

 and herbs are practically identical in each case they have been 

 omitted from these notes. The position of the clumps analysed is 

 indicated on the accompanying map (p. 235). 



Clump 1. — A large Cussonia spicata in the centre. The 

 bark has been almost completely stripped off the lower portion 

 of the trunk. A branch from near the base has fallen and 

 the broken end is covered with earth, indicating the presence 

 of white ants. These appear to be attacking the exposed 

 portions of the roots also. Surrounding the central Cussonia 

 are the following: — Schmidelia erosa, Conibretum kraussii 

 (several trees), Clerodendron glabrum (several trees), Clausena 

 inaequalis, Rhus sp., Cussonia sjjicata (dead and fallen tree). 

 Clump 2. — A smaller clump than No. 1. The oldest tree 

 is quite obviously a large Cussonia spicata. A large branch 

 has recently fallen, and in doing so has broken a young, but 



