ON AKCTIC PLANTS 27 



and analysis of their meaning, brought back new support for 

 Darwin's ideas, wherein was to be found the only intelligible 

 explanation of the problem. 



After enumerating the 762 known Arctic flowering plants 

 with their localities (examining specimens in every possible 

 case), and distinguishing the five Arctic areas characterised by 

 marked differences in vegetation, he traced the distribution of 

 the Arctic plants and their close allies into the temperate and 

 alpine regions of both hemispheres, and showed how this dis- 

 tribution was accounted for by slow changes of climate during 

 and since the Glacial period. 



The five botanical areas differed greatly in the abundance 

 of their flora, while many types were restricted to a north and 

 south range in their own area. Eichest of all was the Scan- 

 dinavian section of the European area, containing three-quarters 

 of the whole Arctic flora, three-fifths of the species and nearly all 

 the genera. Hooker had already pointed out in the Tasmanian 

 Flora that this Scandinavian flora alone of all groups was 

 present in every latitude of the globe. The fuller the investiga- 

 tion, the more clearly all pointed to a southward migration of 

 plants as the Glacial cold devastated the northern lands and 

 a subsequent return northwards at the end of the Glacial 

 period, though in each area certain species had changed during 

 long isolation so as to be botanically defined as closely allied 

 representative species and again in each area the march north 

 had been accompanied by hardy plants from the southern lands 

 temporarily occupied, giving a slightly different character to 

 each area. 



Greenland presented a crucial case. Its flora was scanty ; 

 it possessed scarcely any American species, though so near to 

 America ; and yet, although European in character, it lacked 

 some of the very common Scandinavian types, which ranged 

 far north elsewhere. Its poverty was due not to climate, but 

 to a large abstraction of Arctic types from some other cause. 

 In effect, the plants retreating before the cold found their 

 retreat cut off at the end of the peninsula. Many, having 

 no further refuge, perished. The survivors spread north again 

 with the milder climate, but the sea still sundered Greenland 



