662 A. HESSELBO 



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The Boreal Group, over the whole of Iceland with the 

 exception of South Iceland constitutes the same percentage of the 

 vegetation (S. Icel. 24 %; E. Icel. 30 %; N. Icel. 29 / ; NW. Icel. 31 / 

 and W. Icel. 30 %), and the great majority of the species belong to 

 those which are common everywhere (56 species are common to 

 all the districts of Iceland, with a frequency of 3--4, corresponding 

 to about 60-75 %). 



The Alpine Group likewise shows almost the same percent- 

 age in all the districts (S. Icel. 23 %; E. Icel. 25 / ; N. Icel. 26 %; 

 NW. Icel. 26 % and W. Icel. 20 %) of which about half the number 

 (some 30 species) are common to all the districts. 



The Ubiquitous Group comprises chiefly species which have 

 a great distribution in all parts of Iceland (S. Icel. 34 %; E. Icel. 

 39 %; N. Icel. 38 %; NW. Icel. 39 / and W. Icel. 38 %), 73 of 

 which (67 85 %) are common to all the districts, with a frequency 

 of 3-4. 



The composition of the vegetation as regards percentage is thus 

 very nearly the same everywhere as regards the three last groups, 

 whilst, with regard to the meridional species, the country may be 

 divided into a north-eastern and a south-western part. 



The North-eastern part comprises East and North Iceland 

 as far as Blondudalur. The meridional species play a very slight 

 role in the vegetation here. Two species only, Met~geria fnrcata and 

 Rhacomitrinm aciculare, are common everywhere in this part, and 

 live species, viz. Radnla complanata, Madotheca Cordceana, Catha- 

 rinea undnlata, Mniiim ho r mini and Hypmim commiitatnm, are some- 

 what frequent in East Iceland, but are absent from, or are rare in, 

 North Iceland. 



Some few, principally Boreal and Alpine species, are charac- 

 teristic of North and East Iceland. 



Hijpmim decipiens is very common from Seydisfjordur to Blondu- 

 dalur, but is absent from, or is rare in, the other parts of Iceland. 



Orthothecium chnjseum is one of the most commonly occurring 

 species in the whole of East and North Iceland, but is absent from 

 South Iceland, and is rather rare west of Hunafloi. 



Grimmia ovata has been found only in East and North Iceland. 

 Philonotis tomentella is very common in meadow-ground in North 

 and East Iceland, from Seydisfjordur; but is less frequent on damp 

 rocks in other parts of Iceland. 



