Its Origin , Migrations , and Evolutionary Tendencies. 2 1 3 
Northward from that point it is a broad, flat, sandy belt usually only 
100 feet or so above sea-level, but in Natal it becomes confined to a strip a 
mile or two broad along the coast-line. A considerable number of tropical 
species have not penetrated farther south than Zululand, and this is due 
probably rather to the altered topography than to any general lowering of 
temperature, though the cold current already referred to makes its influence 
felt as far as Port Durnford, where the outward bend in the coast-line turns 
it round. The coast-belt flora is purely tropical to the north of Zululand, 
but in Natal and in the eastern coast-belt of the Cape it has produced large 
numbers of derived endemic species. Mr. R. D. Aitken is carrying out 
a statistical analysis of these on the lines adopted by Willis. Such coast-belt 
endemic species as remain confined to the frost-free localities differ but 
slightly from the tropical ‘ wides \ Other subtropical species are more 
modified and penetrate farther into the colder and drier areas. 
Along the frost-free localities on the flanks of the river valleys the 
tropical flora of the coast-belt has tended to migrate often far inland. 
Dichrostachys nutans, for instance, a characteristic and often dominant 
tropical tree veld species, has penetrated as far as the Lower Mooi River 
area. Recently, while exploring the Umgeni Valley, I was much interested 
to find, at altitudes of 3,000 feet, such typical coast-belt species as. the 
um Doni (. Eugenia cordata , which is the dominant species in hygrophilous 
coast-belt bush), E.gerrardi , Chaetacme aristata , Dracaena hookeriana , and 
Iboza riparia. 
Comparatively few, however, of the actual tropical and coast-belt 
species thus migrate inland. The flora of the Midlands and the Cape 
eastern coast-belt, in response to lower temperatures and drier conditions, 
has been modified and consists of species often closely allied to but usually 
not identical with those occurring in the tropics, or if they do occur farther 
north it is at higher and higher altitudes the nearer to the Equator. We can 
now complete a portion of the main picture. 
Purely tropical vegetation consisting largely of mesophytic trees and 
shrubs with usually simple leaves has invaded South-east Africa along the 
coast-belt and, with diminishing numbers, has penetrated even into the Cape 
Colony south of Natal. Some of the species have migrated far inland along 
the flanks of the river valleys. From this purely tropical vegetation an 
allied modified subtropical vegetation has been derived, which has penetrated 
south as far as the limit of the area of summer rainfall (beyond Port Eliza- 
beth) and has migrated inland at right angles to the coast-line along the 
river valleys and intervening system of ridges. The subtropical flora is 
adapted, on the one hand, to lower temperatures and, on the other hand, to 
drier conditions. This has led to a considerable diversity of growth form. 
A succulent habit is a very common result. Thorn development in response 
to dry conditions is very marked. Evidence is accumulating to show that 
