VI. 



Climate and Floral Reo'ions in Africa. 



o 



ONE of the strangest features of African botany is the extreme 

 poverty of species within the tropics, accompanied by a wealth 

 and superabundance of vegetation, i.e., 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 dift'erent 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. It is a fairly dry country, but does not suffer from drought 

 to any severe extent. On an 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, 



