Its Origin , Migrations , Evolutionary Tendencies . 223 
Cape region of winter rainfall. These form a great line of migration for 
the temperate or mountain element of the flora, which bears a relationship 
to the tropical flora much the same as that of the northern temperate 
regions. Mountains are regions of unstable topography and great climatic 
variations, conditions which appear to favour the production of new 
species. 
7. A comparison of the floral morphology in allied tropical and 
temperate forms shows that in many families the tropical element is the 
older, but in others the reverse is the case, the temperate representatives 
having retained more of the primitive ancestral floral characters. It is 
suggested that the tropical flora has remained more primitive on the 
whole in its growth forms, which are of a rather uniform, woody, meso- 
phytic type with simple bifacial leaves. Herbaceous forms, bulbous and 
tuberous forms, capsular fruits, plants with divided leaves, xerophytes, 
&c., are in general derivate and more characteristic of the temperate 
flora. Floral evolution and vegetative evolution have not always run 
parallel. 
8. While it is considered advisable not to attempt to derive the 
temperate flora as a whole from the tropical or vice versa, yet examples 
are given of tropical genera producing species which have invaded tem- 
perate regions, e. g. Rhus , and of temperate genera which have invaded 
the tropics, e. g. Pelargonium. 
References. 
1. Bews, J. W. : The Plant Succession in the Thorn Veld. South African Journ. of Science, 
Nov., 1917. 
2. : The Plant Ecology of the Coast-belt of Natal. Ann. Natal Museum, iv. 2, 1920. 
3. : An Introduction to the Flora of Natal and Zululand. Pietermaritzburg, 1921. 
4. Brown, N. E. : Euphorbiaceae in Flora Capensis , vol. v. 
5. Guppy, H. B. : Plants, Seeds, and Currents in the West Indies and Azores. 1917. 
6. Sinnott, E. W., and Bailey, I. W. : The Origin and Dispersal of Herbaceous Angiosperms. 
Ann. Bot., xxviii. 4, 1914. 
7. Small, J. : The Origin and Development of the Compositae. New Phytologist, 1917, 1918, 
I 9 I 9- 
8. Willis, J. C. : The Endemic Flora of Ceylon. Phil. Trans., B., ccvi, 1915. 
