296 THE MIGRATION OF BRITISH BIRDS 



and only lingering on a few northern bases in the 

 immediate vicinity of that area it once must have 

 occupied so widely and in such abundance. To describe 

 this flora as either " northern," " Arctic," or " Scandi- 

 navian," is therefore a most erroneous definition. We 

 might, with equal propriety, speak of the "Arctic" 

 element amongst birds, penetrating even to Patagonia, 

 South Africa, Australia, and New Zealand, and even 

 more remote latitudes ; whereas, as we have already 

 seen, such birds are Inter-polar and belong as much to 

 the Antarctic as to the Arctic region. 



There can, therefore, have been no emigration of 

 plants from north to south. The range of the Polar 

 flora has been contracted by extermination (how many 

 times we may probably never know) as far as glacial 

 influences have radiated from either pole ; it has been 

 expanded from such lower range bases as conditions 

 favourable to Polar emigration have returned. We have 

 precisely the same class of phenomena among plants as 

 we have among birds — in many cases identical species 

 in both hemispheres of the more Polar ranging types ; 

 distinct species generically identical, and southern repre- 

 sentative forms, in the case of the more Temperate 

 ranging species — both indicating equatorial centres of 

 dispersal, with little or no isolation or discontinuous 

 range area in the Inter-polar species, but with varying 

 degrees of isolation and discontinuity in those we have 

 already classed as Inter-hemisphere species. It has 

 been said that some botanical genera now characteristic 

 of the Southern Hemisphere appear to have been origin- 

 ally derived from Europe ! Now in the first place some 

 of our most eminent botanists have utterly discounten- 



