Its Origin , Migrations , and Evolutionary Tendencies. 221 
from the ancestral forms, yet there are many examples in the larger genera 
of a tropical or subtropical genus, e. g. Rhus , which has produced temperate 
representatives, or of a temperate or mountain genus, e. g. Pelargonium , 
which has invaded the tropics. The whole family of the Compositae are, 
according to Small ( 7 ), probably montane and temperate in origin, yet they 
have invaded the tropics in considerable numbers. By following the prob- 
able migrations of a genus among the mountain forms, as was done in 
the case of EiLphorbia and Gymnosporia among the tropical-subtropical 
forms, interesting light is thrown on its evolutionary history. 
Pelargonium , unlike Etiphorbia , has somewhat variable floral charac- 
ters, the only really constant generic character being the uppermost segment 
of the calyx forming a ‘ nectariferous tube adnate to the pedicel. The 
petals vary in number (5, 4, or 2) and size, and from being subequal to very 
unequal. In the androecium there are ten filaments, but only from seven to 
two are fertile. Harvey has broken up the genus into fifteen sections, a 
division which other systematists have adopted, e. g. Knuth in ‘ Das Pflanzen- 
reich’jp. 53, 1912. The section Eloarea, consisting of stemless tuberous-rooted 
species, are placed at the beginning as section 1, but though the section is a 
large one, and all typically south-western, it is doubtful whether it should be 
considered the most primitive. The fact that it has a relatively narrow 
range of distribution would tell against its primitiveness, according to 
Willis’s Age and Area law (8). The section Eumorpha has a wider 
distribution from Abyssinia to South Africa. Allied to it is the section 
Peristera , in which the petals are minute, scarcely longer than the calyx ; 
the calyx tube is sometimes nearly obsolete, e. g. in P. fumarioides , 
which is almost an Erodium ; the habit is herbaceous like that of a 
Geranium. This section is the most widely distributed of all, extending 
all over Africa and having one species in India and two in Australia. 
The central species in South Africa is P. grossularioides , which is found all 
over the Cape and is a mountain species in the Drakensberg. Other species 
of the section occur in Namaqualand and the north-west. Considering 
carefully these facts of distribution it would appear probable that the 
ancestral form was a slightly woody or suffruticose type which probably 
arose somewhere in the extra-tropical mountain ranges. The woody habit 
was emphasized in many south-western forms, especially in the section 
Pelargium to which the well-known P. cucullatum belongs. Succulence 
either of stems or leaves is another common feature as an adaptation to drier 
conditions. The stemless tuberous-rooted sections Hoarea and Seymouria 
are all south-western. 
The point of chief interest regarding Pelargonium is the way in which, 
though extra-tropical in its origin, it has produced many species which find 
a place in tropical or subtropical areas. I have listed seventeen species of 
Pelargonium in my ‘ Flora of Natal and Zululand ’ ( 3 ). Two are marked 
