442 J. w. BEws. 



natalensis, the flowers being adapted for pollination by 

 butterflies which frequent the shady places inside the scrub. 



Coast scrub is capable of developing and does develop over 

 practically the whole coast belt, except in the drier, hotter 

 situations, where thorn scrub is the climax type. Grrassveld 

 always gives way to it, as it in turn does to forest. The 

 fact that the existing scrub is so jDatchy is due entirely to 

 man's influence in clearing the ground for the cultivation 

 of sugar-cane. Coast scrub without essential change occurs 

 also on the sand-dunes, where it progresses towards psammo- 

 philous bush or foi^est. Fuller details of the plant succession 

 and further reference to the component species will be given 

 later, when forest is dealt with. 



8. Mangrove Vegetation. 



This type develops on the mud-flats at the river estuaries. 

 One of the best examples of it occurs around Dui-ban Bay, 

 into which the Umbilo and Umhlatusan empty their waters, 

 but it also occurs further south along the other rivers of 

 Natal and the Transkei as far as the Kogha river mouth, 

 south of lat. 32°. At Durban the White Mangrove, 

 Avicennia officinalis (Verbenaceas) (PI. XXII, fig. 1), 

 is dominant around the head of the Bay on the Congella and 

 Umbilo flats. The trees grow isolated or in clumps in the mud, 

 their roots being covered by salt water at high tide. Numerous 

 breathing-roots grow vertically upwards, often through clumps 

 of Salicornia and Chenolea, the pioneer species already 

 described. The other two mangroves at Durban are 

 Hhizophora mucronata and Bruguiera gymnorhiza 

 (Rhizophorefe), both of them somewhat rarer and growing 

 further out along the shores of the Bay. The succession here 

 is very simple. The roots of the mangroves collect and hold 

 the mud brought down by the rivers. The level of the mud- 

 flats consequently rises until the surface is beyond the reach 

 of the salt water. The rivers continue to flood the flats, and 

 ihe water becomes less and less salt. As soon as it becomes 



