342 PLANTS, SEEDS, AND CURRENTS 



bordering the Mediterranean have been able to penetrate the con- 

 tinent and to reach South Africa, the oases of the Desert and the 

 northern slopes of the Atlas representing as a rule their southernmost 

 outposts. Thus of about thirty European Carices that have spread 

 to North Africa only four (C. divisa, vulpina, externa, acutiformis) 

 have reached South Africa by travelling along the length of the con- 

 tinent. There is no prospect with any of the four species that South 

 Africa received them across the Southern Ocean, either from South 

 America or from Australia and New Zealand, since they have not 

 been found there as indigenous plants. All the others, including 

 species like C. pendula, sylvatica, pseudo-cyperus, vesicaria, halleriana, 

 and diluta, have either been checked on the Mediterranean border, 

 or have come to a standstill on the slopes of the Atlas, or have made 

 their last halt in the Libyan oases. 



The Isolation of Africa. — The isolation of Africa, excluding the 

 Mediterranean province which belongs botanically to Europe, is 

 well displayed in the behaviour of the genera Sphagnum and Carex. 

 Though, considering the great area concerned, the representation is 

 poor, Africa holding about 9 per cent, of the known species of 

 Sphagnum and only 4 per cent, of the Carices, yet the species are fairly 

 well distributed. Thus in both cases about half are found in the 

 tropical portion of the continent, and about a third in the southern 

 part. The degree of endemism displayed is also very similar, since 

 both groups of plants are represented by thirty-one species, and of 

 these six extend outside the continent in the case of Sphagnum and 

 seven with the Carices. 



In the following table Africa is compared with the other two great 

 land-masses of the southern hemisphere, South America and Australia, 

 as regards the proportion of its Sphagnum and Carex floras that is 

 not confined to the continent. As far as South America is concerned, 



Comparison in the case of South America, Africa, and Australia, of the 

 Proportions of non-Endemic Species, that is, of Species extending 

 outside these regions 





Sphagnum 



Carex 







Total 



Extending out- 

 side the region 



Total 



Extending out- 

 side the region 



Islands excluded as 

 below named 





Number 



Percentage 





Number 



Percentage 



South 

 America 



110 



11 



10 



81 



29 



36 



Falkland Is., Juan 

 Fernandez, Gala- 

 pagos, etc. 



Africa 



31 



6 



19 



31 



7 



23 



Madagascar, Masca- 

 rene and Atlantic 

 Is., etc. 



Australia 



24 



11 



46 



28 



19 



68 



Tasmania, New Zea- 

 land, etc. 



