20 Bews. — Some General Principles of Plant Distribution as 
A.horrida (A. Karroo ) is commonest and most widespread in South Africa, 
being the most important pioneer tree in dry areas. It is interesting to 
notice its adaptation to more mesophytic conditions on the Natal coast- 
belt. Some species of Acacia , e. g. A. Kraussiana , A. pennata , have 
adopted the climbing habit in the bush. A. caffra has become adapted to 
moister conditions near stream-banks. Like so many of our larger genera, 
Acacia gives excellent opportunities of observing adaptation to various 
ecological conditions, but the majority are extremely xerophytic thorn-veld 
species. The Papilionaceae fall into two fairly well-marked distributional 
groups, an eastern and a south-western with eastern outliers in the south- 
west, e. g. Crotalaria and Vigna , and south-western outliers in the east, e. g. 
Podalyria , Lebeckia , Rafnia . but several large genera are distributed all 
over. The subject is too big to discuss in detail here. 
I must pass over, for the same reason, such large genera as Crassida 
and Mesembriantheimim , though specialists dealing with them could 
illustrate many interesting points with regard to their distribution. 
Rubiaceae . 
This is one of the largest families of flowering plants, and is chiefly 
tropical and subtropical in both the Old World and the New. It is 
particularly interesting to follow the steps of its invasion into S. Africa, 
where it has produced not only large numbers of endemic species, but 
even characteristic endemic genera, e. g. the three belonging to the tribe 
Anthospermeae, viz. Galopina , Nenax ( Ambraria ), and Carpococe , with 2 to 
4 species each, Galopina , from Natal to Swellendam, Nenax , East London 
to Capetown, and Carpococe , Grahamsto.wn to Capetown. The centre of 
distribution of these anthospermous Rubiaceae has been, of course, thought 
to be rather from the south-west than towards it (27, 29). Another endemic 
genus is Burchellia ( B . capensis), which is common from Natal to the Cape, 
but is certainly eastern or tropical in its affinities and origin, belonging as 
it does to the tribe Gardenieae. The distinctly herbaceous genera, e. g. 
Galium , Anthospermum , Oldenlandia (Hedyotis), are generally distributed 
over S. Africa with others ( Pentanisia , Spermacoce , Hydrophylax , a strand 
plant) not quite so far to the south-west. Pentanisia variabilis, as its name 
implies, is extremely variable, and would repay intensive study from the 
distributional standpoint. 
The shrubs and trees are mostly eastern, being very common around 
the margins of the forest and in scrub in Natal, especially on the coast-belt 
(see 12). The herbaceous genera are very distinct in every way from the 
shrubs and trees. Among the latter, the differences one notices as one 
passes from the subtropical Natal coast to the Midlands are very striking. 
Thus Randia dumetorum is a species which extends all through the tropics 
from Hongkong and India to Durban. Another species, R. rudis , is very 
common in the midlands of Natal, but is not tropical. It extends as far as 
