34 Bews . — Some General Principles of Plant Distribution as 
this paper considers present-day tendencies in plant distribution in South 
Africa, directing attention chiefly to the origin and distribution of species, 
but extending the observations also to larger groups. 
2. The present-day conditions in South Africa are summarized and the 
climatic areas are arranged in increasing order of mesophytism : (a) Western 
region, ( b ) Central Karroo region, (c) Cape or South-western region, (d) Sand- 
veld region of the Kalahari, (e) Thorn -veld areas of the eastern side, 
if) High-veld and mountain areas of the eastern side, (g) Coast-belt of 
the eastern side. 
3. Traversing all these areas are certain primitive habitats which are 
occupied by widespread species : (a) Cultivated land, waste places, &c. ; 
(b) lakes, streams, marshes ; (c) sea-shore habitats, mostly sandy ; (d) moun- 
tain ranges; ( e ) drier areas of various kinds. To the north a fairly uniform 
tropical zone crosses the continent and allows tropical species to invade 
South Africa at different points. 
4. A widespread species in the course of its migrations, when it comes 
into contact with conditions different from those which produced it, is often 
capable of giving rise to a new species suited to the new conditions. In 
South Africa, at the present time, such derived species are usually more 
mesophytic than the parent species, but they, may be more xerophytic. In 
many cases, tropical species give rise to temperate species. One widespread 
species may give rise to several derived species or may itself break up into 
several, and, in many cases, the same derived species may have widely dis- 
continuous distribution while its parent form is common all over the same 
area, a fact which suggests the possibility of £ multiple origins ’ or poly- 
genesis. 
5. Certain objections to the evidence for this are discussed and then 
a large number of examples are recorded. These are drawn from as many 
different families as possible, and but for consideration of space could have 
been largely increased. The cohort Tubiflorae is used to demonstrate that 
the same principles may be applied to larger groups, the widespread family 
the Scrophulariaceae having produced the Selagineae chiefly confined to 
South Africa but with outliers elsewhere, and similarly the Myoporaceae in 
Australia, &c. Also attention is directed to the distribution of characteristic 
south-western genera and families and their eastern outliers or connexions 
as throwing light upon the question of the origin of the South African 
flora. 
6. In conclusion, general applications are discussed with special reference 
to (1) plant ecology, (2) the origin of the angiospermous flora of South Africa, 
(3) general phylogeny of the Angiosperms. 
Natal University College, 
Pietermaritzburg. 
November , 1919 . 
