PRESIDENTIAL ADDRESS SECTION C. 67' 



is one of our most distinguished Natalians, and by Dr. van der 

 Bijl, who is stationed here in Durban. 



I have sent a fairly representative collection of freshwater 

 Algae to Miss Stephens and Dr. Fritsch, and a paper dealing 

 with them will, I understand, be published soon. The whole field 

 of Botany is, therefore, being more or less completely covered from 

 the systematic standpoint, and in all branches of the subject new 

 facts and problems are being brought to light. 



I now pass on to deal with the aspect of the subject to which 

 I have given most of my own attention, 



The Plant Ecology of Natal. 



When we seek to describe in general terms the distribution of 

 the vegetation over Natal, the first essential is to distinguish the- 

 various natural plant communities. The first attempts in this 

 direction, which were made by various writers, consisted in picking 

 out characteristic or interesting species which were found in dif- 

 ferent localities. The distinctions between the three main botanical 

 areas, Coastbelt, Midlands, and Drakensberg, were drawn very 

 early by Krauss (1846). Much later Thode entered into greater 

 details on the same lines. Altitude, of course, determines climate 

 in a general way, but altitude in itself is not enough. In the- 

 Midlands there are at least two very distinct climatic areas. For 

 smaller areas soil conditions are sometimes important, but in Natal' 

 as in all great Continental regions the main subdivision must be 

 based on climate. 



As the analysis of the plant communities is proceeded with 

 it is soon obvious that these are not to be considered of the same 

 rank. Some, like various types of forest, are relatively stable, and* 

 except where they are destroyed by man remain more or less 

 unchanged so long as the climate does not change. Other plant 

 communities have a relatively short life in any N locality. They are 

 unstable, and represent what are regarded as stages in the develop- 

 ment of the more stable types which gradually replace them. When 

 we study the development of the vegetation in any area in this 

 way we study what is known as the "Plant Succession." The- 

 most obvious method of doing so is by means of "Quadrats" or 

 "Line" or "Belt Transects." Definite sample areas are carefully 

 marked out, the plants on them counted and mapped, and the 

 changes from time to time noted. Different quadrats are compared 

 and the conditions are varied. The method is a true experimental 

 one, but the difficulties in carrying it out successfully are great. 

 The analysis of the habitat factors even with the assistance of 

 instruments is difficult. One cannot be quite sure that two distinct 

 quadrats, which are to be treated differently, are alike in all 

 respects (especially with regard to soil conditions) to begin with, 

 or whether each agrees with "control" quadrats. Nevertheless 

 the results to be obtained by this method are very valuable, though, 

 for slow-growing types, a long period must elapse before any results 

 are obtained. 



Another method of analysing the plant succession is bv means 

 of observation and deduction — the method of the geologists. It 



