112 



would form a most interesting subject for detailed study. 

 Each, stage has a certain degree of stability of its own, and 

 each is being constantly repeated in the initial stages of 

 various siib-seres. They may be classified as follows: — 



(a) Lichen Colonies. These colonize bare rock surface and 

 consist of crustaceous and foliose types. Over the whole of 

 the Eastern side, though examples are abundant, there is no 

 extensive lichen development as there is on the Western side. 

 The Lichens are a group which have been very little studied 

 in South Africa. 



(b) Cyanophyceae Colonies. These are very extensively 

 developed, especially at higher altitudes, and consist of species 

 of SchizothfLv, Stigonema, Gloeocafsa, Calothrix, etc., which 

 form black coverings over damp rock surfaces. 



(c) Colonies of Mosses and Hepatics. This type has 

 recently been dealt with by Simi. Mosses and Hepatics are 

 of considerable importance in preparing a seed bed for higher 

 plants which soon follow. 



(d) Litliophiloas Colonies of Ferns and Flowering plants. 

 It is impossible to give anything approaching an exhaustive 

 account of these. They are far too numerous and varied. 

 The following are a few common examples : — 



(1) Selaginella rupestris often forms loose mats over rocks 

 which are periodically wet, but which often remain dry for 

 months, when the mat becomes dry and shrivelled. A loose 

 shallow soil gathers underneath. 



(2) Cypenis rupestris grows over soil, which is an inch 

 or so deep, and wet. The Selaginella and Cypenis often mix. 



(3) Other Cyperaceae, such as species of Bulhostylis 

 (B. collina, B. striatella) or Fimbristylis, also form pioneer 

 colonies on rocks. 



(4) Crassula colonies are numerous and widespread. 



(5) Mesemhrianthemuv2 colonies. 



(6) Cyanotis nodiflora, a very frequent pioneer on rocks; 

 loose and straggling in its growth. Such species rarelj' form 

 pure growths. They ar* quickly followed by numerous others, 

 e.g., species of Oxalis, Hypo.ris, and other small bulbous or 

 tuberous forms. The j^ioneer grasses are usually very early 

 arrivals. 



1. Sim, T. E. "The Geographical distribution of Bryophyta in S. Africa." 

 S. A. Journal of Science, 1918. 



