Some General Principles of Plant Distribution as 
illustrated by the South African Flora. 
BY 
J. W. BEWS, M.A., D.Sc., 
Professor of Botany in the Natal University College. 
Introduction. 
( FEB 10 1921 
T HE geographical distribution of plants, which has been described by 
Darwin (20), in one of his letters to Sir Joseph Hooker, as ‘ that grand 
subject, that almost keystone of the laws of creation has been studied from 
many different standpoints, and, with the increasing interest in plant ecology, 
is now attracting more and more attention. Darwin’s own position is sum- 
marized in a single sentence in the ‘ Origin of Species ’ (16, p. 360) : c If 
the difficulties be not insuperable in admitting that in the long course of 
time all individuals of the same species, belonging to the same genus, have 
proceeded from one source, then all the grand leading facts of geographical 
distribution are explicable on the theory of migration, together with sub- 
sequent modification and the multiplication of new forms.’ The general 
progress of the study of plant distribution since the publication of the 
‘ Origin of Species’ has been dealt with by Thiselton-Dyer (20), from whose 
paper a few extracts will be taken. ‘ If Darwin laid the foundations, the 
present fabric of botanical geography must be credited to Hooker. It was 
a happy partnership. The far-seeing generalizing power of the one was 
supplied with data and checked in conclusions by the vast detailed know- 
ledge of the other.’ Hooker’s views were given in the ‘ Introductory Essay 
to the Flora of Tasmania ’ (27) and in the ‘ Distribution of Arctic Plants ’ — 
publications which were, according to Thiselton-Dyer, ‘ only less epoch- 
making than the “ Origin ” itself’. After Darwin, Wallace carried on the 
task of investigation, and his views are given in his well-known work 
‘ Island Life ’ (35) and as late as 191 1 in ‘ The World of Life ’ (36). 
Both Wallace and Darwin objected to invoking geographical change 
as a solution of every difficulty. They believed in the general stability and 
permanence of our continental areas, while admitting ‘ wonderful and 
repeated changes in detail’ (35, p. 101). Their views in this respect 
received great support as the result of the Challenger expedition, which 
furnished proof that the floor of the ocean basins has no real analogy 
[Annals of Botany, Vol. XXXV. No. CXXXVII. January, 1921.] 
B 
