PRESIDENTIAL ADDRESS SECTION C. 77 



confined to the mountain regions of Natal, in contrast to the great 

 Andropogon, Fanicum, Aristida, Eragrostis, Sporobolus series 

 which are so abundant at lower altitudes. 



While the temperate flora of the Drakensberg and the tropical 

 flora of the coastbelt and certain midland river valleys are clearly 

 very distinct, the vegetation of the midlands as a whole is not so 

 easily analysed. The dominant species in the subclimax and climax 

 communities, i.e., in grassveld and in forest, are subtropical in their 

 affinities. The grasses, trees, and shrubs are nearly all clearly to 

 be connected with other purely tropical species. Very often coast- 

 belt (tropical) species and midland (subtropical) species may be 

 paired in a rather striking way. Earlier stages of the plant suc- 

 cession are, however, not so clearly tropical or subtropical. The 

 vernal aspect societies in the grassveld are extraordinarily abundant, 

 and comprise a very high percentage of the total flora. The 

 Compositae and the bulbous Monocotyledons are by far the most 

 important, and they are also best represented on the Drakensberg. 

 It is true that they are common enough also on the coastbelt but 

 not in the scrub and forest (the subclimax and climax vegetation) 

 of the coastbelt. There they are relatively scarce. It would 

 appear, therefore, that the earlier stages of succession in the mid- 

 lands, including the numerous spring flowering plants of the grass- 

 veld, are to be reckoned as rather temperate than tropical in their 

 affinities and to be connected with the mountain flora rather than 

 with that of lower altitudes. This tentative conclusion would seem 

 to be supported by the recent experimental work of MacDougall* 

 in America on the interchange of species from one environmental 

 complex to another. He found that species from cool regions may 

 be more easily established in warm places than the reverse and 

 montane plants may come to the seashore more easily than plants 

 of maritime zones may spread over a mountain, and also that dis- 

 semination movements are seen to be freer from regions presenting 

 climatic extremes to more equable climates. 



Ecology, particularly from the successional standpoint, has 

 many other useful applications apart from enabling one to classify 

 the vegetation units, to understand, and often to control their 

 development and to explain their distribution and their response to 

 environmental factors. 



The plants themselves, apart from the communities to which 

 they belong, may be studied, compared, and classified, and the 

 experimental developments of physiological ecology are full of 

 promise. 



Life Forms and Plant Succession. 



The earliest attempts, such as that of Humboldt, at classifying 

 the growth forms of plants were simply physiognomic. Re- 

 semblances were noted in the members of the same group, and 

 heathforms, palmforms, grassforms, etc., were recognised. Of the 



* MacDougall. D. T. "The Reactions of Plants to new Habitats." 

 Ecology, II, 1921. 



