160 H. JONSSON 



Occurring in E. Iceland Occurring in S. Iceland 



and absent from E. Iceland. 

 Boreal Communities and Asso- 

 ciations. 

 The Pelvetia-Fucus-spiralis-heW. 

 The Community of Corallina. 

 The Fucus serrafas-association. 

 The Phymatolithon-polymorphum- 

 association. 



and absent from S. Iceland. 



Arctic Associations. 



The Monostroma groenlandicum- 



association. 

 The Polysiphonia arcfa'ca-associa- 

 tion. 



Subarctic Association. 

 The Laminaria fceroensis-associa- 

 tion. 



Further it should be pointed out that the epiphytic vegetation 

 on Laminaria hyperborea is quite infinitesimal in E. Iceland, but 

 very luxuriant in S. Iceland. 



Of E. Iceland species which are important to the vegetation, 

 Laminaria nigripes, Turnerella Pennyi and others are absent from 

 S. Iceland. Of S. Iceland species which play a prominent part in 

 the vegetation a great many are wanting in E. Iceland (see Part III). 



The Zoster a-association requires to be described separately. 

 It belongs properly to SW. Iceland. Zostera is also known to occur 

 in E. Iceland and it is possible that it forms associations there, but 

 they are probably far more limited in extent than those in SW. 

 Iceland. Zostera has not been found in S. Iceland itself, which is 

 probably due to the fact that a favourable substratum for it is 

 wanting there. 



If we now leave the Zosfera-association out of consideration, as 

 the lalter does not occur in S. Iceland, and confine our attention 

 to the above-mentioned communities and associations which are 

 found in the one district but are absent from the other, then it is 

 seen that at any rate some of them characterize the vegetation to a 

 considerable extent. 



The Monostroma groenlandicum-association, as already 

 mentioned, is peculiar to E. Iceland and has a considerable exten- 

 sion in several places there. It is not found in S. Iceland. Mono- 

 stroma groentandicum occurs sparingly both in N. Iceland and NW. 

 Iceland, therefore it is possible that this association is not exclu- 

 sively confined to E. Iceland. As the community of filiform algae is 

 commonly distributed both in E. and S. Iceland and green filiform 

 algae occur very luxuriantly in S. Iceland, the absence of M. groen- 

 tandicum from the latter place is of no essential importance to the 

 vegetation as regards appearance. 



