VI. 
Climate and Floral Regions in Africa. 
NE of the strangest features of African botany is the extreme 
poverty of species within the tropics, accompanied by a wealth 
and superabundance of vegetation, 7.c., of individuals, which can be 
hardly realised without actual observation. On the other hand, 
outside the tropics, both the number of species is astonishing (some- 
times there are more known from a given area than is the case 
anywhere else in the world), and again, the number of individual 
plants on a given area is exceedingly small as compared with the 
tropics, and never shows the same extraordinary luxuriance. 
The reason for this difference may be partly appreciated by 
noticing some of the distinct climatic conditions which exist in tem- 
perate Africa; each different climate maintaining, of course, its own 
set of plants. 
Travelling in imagination along North Africa, from Gibraltar to 
Egypt, we notice the following changes. First, in Morocco, 
Algiers, and part of Tunis (roughly speaking, on the Northern 
Mediterranean side of the Atlas chain and its continuations, which 
run out in the sea near Tunis) we find ourselves in a Mediterranean 
climate. Itisa fairly dry country, but does not suffer from drought 
to any severe extent. Onan Algerian hillside, one sees numerous wild 
olive trees, many bulbous plants, and small shrubby perennials, while in 
sheltered places many annuals occur, but there is an almost complete 
absence of thick sward and the dense growth which one notices, for 
instance, in England. There is nothing like the crowding and 
struggle for existence which goes on in temperate Europe; every 
plant seems, as a rule, able to spread out, and the tint of the land- 
scape is that of the underlying soil, ‘often red, with a sort of grey- 
green haze, due to the scanty vegetation; the number of species is, 
however, fairly large. An examination of the plants themselves shows 
that they are mainly Mediterranean forms with numerous endemic 
species or varieties, whose origin from European species or their 
ancestors is intelligible enough if we remember the years that have 
elapsed since Tunis was in free land communication with Sicily, 
and since the Straits of Gibraltar were formed. 
In Tripoli and the Bay of Syrtis, we are, in the desert of Sahara, 
exposed to the most severe and protracted drought. The plants that 
exist are very isolated indeed, in most places a foot or more apart, 
