SUMMARY AND CONCLUSION 301 



difference of conditions prevailing in the two Temperate 

 zones of the earth, than in the entire Polar zones (either 

 by altitude or latitude), is reflected in the species occupy- 

 ing them. In Polar zones conditions are very similar 

 throughout, — hence we find (especially as regards floras) 

 various forms preserving specific identity throughout 

 vast areas ; in Temperate zones conditions are almost 

 endlessly varied, so that species have been modified and 

 multiplied in conforming to such varying conditions, 

 and the equatorial range base is very frequently only a 

 generic one. Thus we find in the floras of Australia 

 and Europe that species of a Temperate zone in Europe 

 are represented in Australia by very distinct species. 

 Both must have sprung from a common equatorial range 

 base (Borneo, the Moluccas, and New Guinea), one 

 portion of a species emigrating as far north as Europe, 

 the other portion as far south as Australia. The con- 

 ditions which each set of individuals experienced were 

 totally different, and modification of a specific value was 

 produced, although in many cases they have both 

 managed to retain their generic affinity. 



When tested by the distribution of plants in Africa 

 these facts assume even greater significance and sugges- 

 tiveness. According to Dr. Wallace, there are no less 

 than 60 genera of North Temperate plants in South 

 Africa, none of which occur in Australia, and but few of 

 the species characteristic of Australia, New Zealand, and 

 Fuegia are found there. South Africa is now isolated 

 from all the great southern land masses, and appears to 

 have been so for a comparatively long period, a fact 

 which has not only arrested the southern emigration of 

 plants, but caused much modification. The Temperate 



