2J4 Bews. — The South-east African Flora : 
compound or divided leaves are far more common in derived subtropical 
species than in the purely tropical. The herbaceous habit is often deriva- 
tive. 
Migration and Evolution: Comparison of Tropical and 
Subtropical Forms. 
The accepted principles of phylogeny on the whole support the view 
adopted, viz. that the subtropical flora has been derived from the tropical, 
but, as we shall see later when the temperate element is also compared, 
floral evolution has not always run parallel to that of the vegetative 
morphology. An examination of practically all the families has been made, 
but considerations of space prevent our dealing with more than a few com- 
parisons here. The following families are chosen at random : 
Flacourtiaceae. The tribe Erythrospermeae with the perianth leaves 
spirally arranged is the older and widespread in the tropics, having one 
genus, Raw sonia , which reaches Natal. The other nine South African 
genera are subtropical and more advanced in flower structure, having 
perianth leaves whorled and usually petals present as well as sepals. 
Violaceae. The tropical-subtropical Rinoreae (shrubs and trees with 
nearly regular flowers) are to be contrasted with the subtropical and tem- 
perate Violeae, herbs with irregular flowers. 
Loranthaceae. Loranthus has an hermaphrodite and less reduced, and 
therefore being parasitic probably an older, type of flower than Viscum. 
Loranthus is distinctly more tropical than Viscum. 
Thymelaeaceae. Octolepis is the most primitive type, with a flat 
receptacle, and is purely tropical (seven species in West Africa). Peddiea is 
an East African tropical-subtropical genus with a two-celled ovary and fruit 
a drupe, not so primitive as Octolepis , but more so than all the other South 
African genera of shrubs, undershrubs, and herbs which have the ovary one- 
celled. There are certain pairs of families which might be compared and 
contrasted to illustrate the same thing, e. g. Apocynaceae, more tropical and 
relatively more primitive, and Asclepiadaceae, distinctly more subtropical 
or even temperate and relatively more advanced in floral morphology. 
Araliaceae and Umbelliferae, Myrsinaceae and Primulaceae are similar 
pairs. 
Euphorbiaceae. This family is clearly tropical in origin, and the most 
recent and highly developed derivative types like Euphorbia have pene- 
trated farthest into the colder and drier regions, while the tropical types, 
though they have broken up into great numbers of distinct genera, have 
retained more of the primitive floral characters. The genus Euphorbia with 
about i, coo species has a remarkably uniform floral structure, and very 
extreme vegetative variation from tiny annual herbs up to large trees over 
sixty feet high. Variations in floral structure are confined to the involucral 
