Transition to the High Mountains of Tropical Africa. 535 
enabled any seed carried from the northern temperate zone to this 
continent to germinate and to grow. 
The differences to be seen in most of these highland forms, as compared 
with their relatives of the northern temperate zone, are always in harmony 
with the different climatic conditions. The temperature of the alpine 
region of Kilimanjaro or Ruwenzori may be somewhat like that of our 
high Alps during the summer time ; but there is this great difference 
that, in the snow-region of Africa, the ground is free from snow several 
months longer than in the Alps, and that, during the dry period, the 
strong insolation, even when acting only a few hours of the day, dries 
up the soil very much. Only in crevices and small ravines more favourable 
conditions exist for the development of turf-forming hygrophilous plants 
such as are so abundant on our alpine meadows. The variety of such 
plants is at the present time (and has been also during the pluvial period) 
much inferior to that on the mountains of the northern temperate zone, 
where large continental areas allowed a rich development of the plants 
wanting only little warmth for existence, and where repeatedly climatic 
changes were responsible for far-reaching migration of the highland forms 
originally evolved in the various centres of evolution. 
There is also very little in common between the alpine flora of the 
lofty mountains of Africa and the highland flora of the Mediterranean 
mountains, where the arctic-alpine plants are wanting or very scarcely 
represented. A number of genera, it is true, are to be found also on 
the mountains of Tropical Africa, viz. Trifolium , Scabiosa , Cephalaria , 
Campanula , Crepis , Hypericum , Micromeria , Anemone , Car duns, Centaur ea, 
Helichrysum , and a few others. Of Helichrysum y a few species are marked 
even by their woolly tomentum. But we do not in the least find the 
extraordinary amount of woolly or tomentose and spinous perennials so 
conspicuous on the mountains of Asia Minor and Central Asia, on the 
mountains of Greece, and even on the Sierra Nevada; nor are the leafless 
broom-like shrubs prevailing in the hiliy parts of the Mediterranean 
countries to be seen on the mountains of Tropical Africa. It is obvious 
that this feature is explained by the much more intense dryness of the 
atmosphere and of the soil during the Mediterranean summer. From 
the same cause, only a few types of the steppe may be seen ascending 
to the alpine region in Tropical Africa, although access seems easy enough. 
How very different in the high mountains of Asia Minor, where the 
types of the steppe ( Astragalus , Cousinia , Artemisia , Statice, Labiatae, 
Boraginaceae, Cruciferae, ’ Umbelliferae, bulbous plants) prevail to an 
astonishing extent! In Tropical Africa we find only grasses of the steppe 
ascend to higher altitudes. Also Ericaceae and small-leaved shrubs of 
a similar habit are more abundant, but these belong to types more or 
less developed in Southern Africa. 
