32 Bezus. — Some General Principles of Plant Distribution as 
(1911, 36 ), that they create more serious difficulties than they are supposed 
to explain. After a half-century of thought and work on this and allied 
subjects, Wallace had lost none of his vigour in denouncing theories of 
continental extensions. He concludes by saying, c I believe it can now be 
truly said that, no stratigraphical geologist accepts the theory of frequent 
interchanges of continental and oceanic areas, which are so hastily claimed 
by palaeontologists and biologists to be necessary in order to overcome 
each apparent difficulty in the distribution of living or extinct organisms, 
and this notwithstanding the number of such difficulties which later dis- 
coveries have shown to be non-existent ’. 
The other view of the origin of the southern floras is that of Thiselton- 
Dyer and Guppy, which has already been fully explained. A northern 
origin for many important elements of the South African flora has of course 
always been admitted. With regard to the south-western flora, a sufficient 
number of families and tribes, e.g. Proteaceae, Ericaceae, Rutaceae, Verbe- 
naceae, Restionaceae, Gramineae, Selagineae, and large genera, e.g. Heliophila , 
Muraltia , Pelargonium , Oxalis , Erica , Cliff or tia^ Selago , Danthonia , Penta- 
schistis , and many others, have been dealt with in our general survey to show 
that in practically every case, while the greatest concentration is in the south- 
west, and within that region in such * cul-de-sacs 5 as the Cape Peninsula, 
yet there are eastern and northern outliers or relatives which in many cases 
extend right through the tropics to Europe and Asia. 
It must of course be admitted that these are very meagre when 
compared with the rich development of species in the south-west, but. at 
the same time, there are no real grounds for the common assumption that 
the area where a family or genus is now best represented is necessarily the 
centre where it has originated. If the primitive ancestors of the south- 
western flora came from the north, there is no need to assume that the 
original immigrants were very numerous. They have left few descendants 
along the track of their invasion because conditions there are not generally 
suited to them, but when they reached more temperate areas in South 
Africa they multiplied exceedingly and produced many divergent types in 
the course of their differentiation. 
One reason, perhaps the chief reason, why the second view appears the 
more acceptable is that it represents conclusions which can be reached by 
applying the principles which we can study at the present day within 
South Africa with regard to the origin of species. If we simply extend 
the time and the area, we can apply the same principles to- the genera, 
tribes, and families, and the example of the origin of the Selagineae, at 
present mostly South African, and in South Africa mostly south-western, 
from the widespread Scrophulariaceae clearly throws light upon what has 
happened during the past. 
The view-point adopted in this paper is also a useful one in connexion 
