24 



Nr. !<. c;. H. OsTKNi ei-d: 



it luaix'sl to (iretMihind. II" it is louiul tor instnncc, iii Arctic 

 North America and Arctic Asia, it is takcii as American, 

 whilc a species occiiiring in Europe, possibly in Iceland, 

 and also in western North America, is regarded as Euro- 

 pean. The categories cmployed are as follows: 



A. Species l'ound in North America, but not in Pairope. 

 li. Species ("ound in North America and Icehind, l)ut not 



in other parts of Europe. 

 C Species found in North America and Europe, i)ul not 



in Iceland and Scandinavia. 

 I). Species found in North America, and in PZurope, but 



not in Iceland. 



E. Species found in Europe, but not in eastern North 



America. 



F. Species found in arctic Europe, l)ut not in Scandinavia 



and Iceland, nor in N. America. 



G. Species found in North America, Iceland and Europe 



(circumpolar species). 

 H. Species not known outside Greenland (endemic species). 



FolloNving the general geographical distribution of the 

 species, I have thereupon divided them into three phyto- 

 geographical types (elements). This must of course always 

 be done according to the writer's personal judgement, as 

 there will inevitably be some doubtful cases. I have chosen 

 to divide as follows: 

 Ap High -arctic species, i. e. those found almost ex- 



clusively in arctic regions and able to thrive under 



very severe conditions. 



A^. Arctic species, i. e. those having their main area of 

 distribution in the arctic regions, but also found far 

 outside these. 



