AN (ECOLOGICAL SURVEY OF THE MIDLANDS OF NATAL. 529 



the plant formations in Natal. It is found in all the main 

 river valleys wherever the rivers have cut through so steeply 

 as to leave such rocky slopes. In the area at present under 

 consideration it occm-s below Howick, but the best examples of 

 it in the neighbourhood are further down the Umgeni and 

 just outside the area mapped. The valley of the Tugela is 

 richer still in this type. A rubber company has been formed 

 to work the rubber obtained from Euphorbia tirucalli, 

 and it has been estimated that there are at least twelve 

 million specimens of that tree in the Tugela valley alone. 

 The estimate is probably a fairly accurate one (see PI. XL VI). 



Although thorn trees also occur in this formation, yet its 

 xerophytism is shown rather in succulence. The euphorbias 

 a,nd aloes may be taken as the typical members. There are 

 few gi-asses. Those that do occur are of the low veld, stony 

 hillside type already described. 



The various plant formations of hillsides might be grouped 

 as follows : 



(1) High Veld Region. 



(a) South exposure : 



Close bush. Bush clearing. Andropogon veld. 



(b) North exposure : 



Mixed xerophytic trees and shrubs (inter- 

 mediate between close bush and thorn veld). 



(2) Low Veld Region. 



(a) South exposure : 



Thorn thickets (similar to thorn veld but 

 denser) . 



(b) North exposure : 



Extremely xerophytic trees and shrubs. Succu- 

 lents. Very few grasses. 



5. ALPINE PLANT FORMATION. 



The Zwaartkop mountain has an altitude of 4758 feet, which 

 is the highest in this area. The higher altitude has brought 



