SUMMARY AND CONCLUSION 299 



soon as conditions became favourable. It is said by Dr. 

 Wallace (referring to the Andes) that there are " between 

 sixty and seventy northern genera in Fuegia and 

 Southern Chile, while about forty of the species are 

 absolutely identical with those of Europe and the Arctic 

 regions " ; and further, " as only a few of these species 

 are now found along the line of migration [emigration], 

 wc see that they only occupied such stations tempor- 

 arily." There is not a shadow of evidence to support 

 the latter assumption of short occupation. Species that 

 reside at high elevations on mountains have necessarily 

 a somewhat restricted area of distribution, and would 

 be more quickly exterminated in such localities than in 

 lower and wider areas ; for, as Dr. Wallace himself 

 suggests, the raising of the snow-line, due to glacial 

 causes, would not only reduce their area of distribution, 

 but ultimately cause their extinction even in the very 

 centres of their dispersal. 



With regard to the actual route which this Inter-polar 

 flora followed, north or south to either Polar continent, 

 nothing need be said ; but we cannot accept Dr. 

 Wallace's conclusions, that when the South Polar con- 

 tinent became glaciated " these plants would be crowded 

 towards the outer margins of the Antarctic land and its 

 islands, and some of them would find their way across 

 the sea to such countries as offered on their mountain 

 summits suitable cool stations ; and as this process of 

 alternately receiving plants from Chile and Fuegia, and 

 transmitting them in all directions from the central 

 Antarctic land, may have been repeated several times 

 during the Tertiary period, we have no difficulty in 

 understanding the general communitv between the 



