1 6 Bews. — Some General Principles of Plant Distribution as 
genera distributed over South Africa, tend to fall into a group by them- 
selves, distinct from the south-western. The genus Dombeya is tropical 
in its affinities. The South African species all come close together. 
D. natalensis and D . rotundifolia are both common in the coast and mid- 
lands of Natal (the latter also in Rhodesia). D. dregeana, which extends 
from Natal to Uitenhage, only differs in the flower-buds, leaves, and 
involucral leaflets from D. natalensis. To the north, in the Transvaal, 
there are six other species, and the genus is still better represented in the 
tropics. We thus see, as in so many other cases, the various steps of 
invasion from the tropics into South Africa, with consequent modification. 
While the genera Hermannia and Dombeya afford perfect examples of 
the working of our general principles, when we turn to the genus Sterculia , 
as represented in South Africa, we find a case of the most extraordinary 
isolation. The genus is most abundant in tropical Asia, but there are 
seven species in the ‘Flora of Tropical Africa’ and one, S', mutex , in the 
Lydenburg district of the Transvaal. S. Alexandri (Harv.), however, occurs 
completely isolated near Uitenhage. Harvey says it is allied to S.foetida, 
but differs in various characters, and adds,‘ No one seems to have met with 
it but Dr. Alexander Prior, who found but a solitary tree in a narrow kloof, 
somewhere among the Van Staadem Mts., a locality rich in interesting plants 
and probably still concealing other novelties.’ Schonland (30) refers to 
its complete isolation, but he does not say whether it has been collected since. 
Tiliaceae. 
The genus Grewia is a great tropical African genus which has pro- 
duced species capable of invading South Africa. Grewia occidentals 
extends from Abyssinia to the Cape Peninsula. It is a typical pioneer in 
the xerosere, important in establishing scrub and forest. G. caffra , which is 
common in the Natal coast-belt bush, is probably derived from it though 
specifically distinct, and many of the other rare species might also be con- 
nected. No better example could be found of the first of our categories, but 
cases of discontinuous distribution would be discounted as examples of 
polygenesis, because of the edible drupes. The genus Sparmannia has 
5. abyssinica not known outside Abyssinia, but apparently intermediate 
between the two South African species S', africana and S. palmata. 
Geraniaceae . 
Pelargonium is a large and characteristic Cape genus with a few out- 
liers in tropical Africa, western Asia, and Australasia. We find that 
P. multibracteatum from Abyssinia is closely allied to P . alchemilloides 
from the Transvaal, Natal, and the Cape, the latter being a variable species. 
P . flabellifolium is common in the upper districts of Natal and is also 
recorded for Angola and the Transvaal. There are seventeen species 
altogether in Natal and ten in the Transvaal, but the largest section of the 
genus, the section Ho are a, is altogether south-western. Many of the species 
