MARINE ALGAL VEGETATION 161 



The Polysiphonia arctica-association is of importance 

 as regards the appearance of the sublittoral vegetation in E. Iceland. 

 This association does not occur in S. Iceland, but a corresponding 

 one occurs, which is however far less luxuriant, composed of Poly- 

 siphonia urceolata. 



The Laminaria fseroensis-association is known to occur 

 only in E. Iceland. This association is probably more widely dis- 

 tributed along Iceland than is at present known; the species occurs 

 at any rate in N. Iceland. But I think that this species will hardly 

 be found along the coast of S. Iceland owing to the fact that shel- 

 tered localities are wanting there. 



The Pel vetia-Fucus-spiralis-belt is most commonly dis- 

 tributed in S. and SW. Iceland, and composes there the upper part 

 of the Fucacecp-eommunity. As this belt is absent from E. Iceland 

 there is a considerable difference in the appearance of the upper- 

 most part of the Fucacece-community in the coastal districts in 

 question. Fucus spiralis is, however, found in E. Iceland. 



The Community of Corallina is also peculiar to S. and 

 SW. Iceland and absent from E. Iceland. This community, or the 

 Corallina-Gigartina belt, is very luxuriant and often of considerable 

 extent in S. Iceland (and SW. Iceland), owing to which the semi- 

 littoral vegetation in E. Iceland and in S. Iceland differs highly in 

 character. 



The Fucus serratus-association is poorly represented in 

 S. Iceland, but it is luxuriant in a single locality in SW. Iceland. 

 As Fucus serratus is rare, and somewhat resembles in appearance 

 the large, broad-leaved forms of Fucus inflatus which are common 

 everywhere, it plays only an inconsiderable part as regards the 

 appearance of the Fucacere-community. 



The Phy matolithon poly morphum-association is pe- 

 culiar to S. Iceland, but as other crustaceous, calcareous algae occur 

 in E. Iceland in a similar manner though less luxuriantly, the ab- 

 sence of Phy matolithon polymorphum is of no essential importance 

 as regards the appearance of the crustaceous-alga-vegetation. 



From what has been stated above it is evident that the occur- 

 rence of the Pelvetia-Fucus-spiralis-be\t and the Corallina-Gigartina- 

 belt in S. Iceland (and SW. Iceland) gives to the littoral and semi- 

 littoral vegetation of the southern district a character different from 

 that of E. Iceland. 



The Botany of Iceland. I. \\ 



