2 22 
Bews. — The South-east African Flora: 
c doubtful ’, five are purely mountain, but the others are found either in the 
Midlands or even on the coast- belt. P. aconitiphyllum is the commonest. 
It is, like the others, adapted to grassland conditions, and forms one of the 
commonest of the ‘ vernal aspect societies ’ in subtropical grassveld. This 
illustrates again the temperate affinities of those vernal aspect societies. 
In the above account the South-east African flora as a whole has been 
dealt with in a general way, and the details mentioned have been used 
as examples. More detailed investigations on the above lines, in which our 
modern knowledge of morphology, physiology, and physiological anatomy 
is being utilized, are in progress at this centre, and the results appear likely 
to be very interesting. 
Summary. 
1. South-east Africa has a flora composed of two distinct elements : 
(a) a tropical-subtropical element, and (b) a temperate or mountain element. 
The study of various lines of migration throws light on the origin of these 
elements and also on many questions of evolutionary history. 
2. The various trees and shrubs composing the woodland plant com- 
munities are distributed mainly by birds and other animals, and they tend 
to migrate most rapidly along the main river valleys at right angles to the 
coast. This river valley migration, however, is the final step in a general 
migration from the north along the coast-belt. 
3. The tropical flora has invaded South-east Africa and remains 
distinctly tropical on the coast-belt. The numbers of tropical species 
diminish southwards, being gradually replaced by allied subtropical species. 
A few of the tropical species have migrated for considerable distances inland 
along the valleys, but in general with rising altitude, lower temperatures, 
and drier conditions the flora becomes subtropical. 
4. A comparison of the floral morphology in allied tropical and sub- 
tropical forms shows that the former is older and the latter derivative. 
Succulence, spinescence* and other forms of xerophytism in response to 
drier conditions are characteristic of the subtropical flora, as is illustrated by 
the evolution of the genus Euphorbia. Sometimes derived and recent 
species may be, on the one hand, more xerophytic and, on the other hand, 
more mesophytic, as in the genus Gyninosporia . 
5. The species composing the South-east African grasslands are mostly 
wind -distributed and lines of migration are not so easily determined. The 
grasses are tropical or subtropical and also the autumnal aspect societies. 
Vernal aspect societies, however, while largely endemic, and of a type 
by themselves, have on the whole more affinity with the temperate element 
of the flora. 
6. Great mountain ranges run parallel to the eastern coast of the 
African continent across the tropics and connect with the south-western 
