366 ECOLOGICAL FACTORS, ETC. 



(i) The arctic group, with its southern European border in north 

 Norway and Iceland, although in America the group may extend as 

 far south as Cape Cod. 



(2) A subarctic group, the species of which are common in the 

 Arctic sea and the cold boreal area of the Atlantic as far south as 

 western France. 



(3) Boreal arctic group. These species are common in the 

 Arctic Sea and the boreal area of the Atlantic as far south as the 

 Atlantic coast of North Africa, some perhaps penetrating even 

 farther south. 



(4) A cold boreal group which is of more limited distribution, 

 extending northw^ards from western France to south Iceland and 

 Finland, with outlying species penetrating in the south to the 

 Mediterranean and in the north to the White Sea and Sea of 

 Murman. 



(5) A warm boreal group, the species of which extend as far 

 south as the Mediterranean and Atlantic coast of North America, 

 some perhaps even farther south. Their northern limits are to be 

 found in south Iceland, the Faeroes, north-west Norway and 

 Scotland. 



Although Iceland is so far north, nevertheless the flora is pre- 

 dominantly boreal because 54 % belong to the last three groups. If 

 the different districts of Iceland are compared with neighbouring 

 floras it is extremely interesting to see how the floras of the various 

 parts of the Icelandic coast show resemblances to floras from a 

 number of widely separated areas. 



Another interesting feature in geographical distribution, which 

 has been established by Setchell (1920), is the relation of the 



