- 



106 H. JONSSON 



Reykjavik, especially later in the summer, it frequently has a yel- 

 lowish-brown tinge. 



These associations, owing to local conditions, naturally are not 

 found everywhere along the coasts. At times they are all present, 

 and then generally in the succession here recorded ; at other times 

 only one or another is present. Thus, in some places, the upper 

 limit of the marine algal vegetation is indicated by the Ulothrix- 

 association, and in others by the Bangia or the Porphyra associa- 

 tion; in places the entire community is absent, and then the boun- 

 dary is marked by Pelvetia, Fucus spiralis or other Fucacece. 



A comparison with the adjacent coasts shows that this community 

 is found both in Greenland and in the Faeroes though it does not 

 behave in quite the same manner in both places. In Greenland a Mono- 

 stroma groenlandicum- association is found which is composed of 

 Monostroma groenlandicum, Ulothrix flacca and Urospora mirabilis, 

 all intermixed with Bangia fuscopurpurea. This association occurs 

 in the middle part of the littoral zone. A Porphyra umbilicalis- 

 association occurs also in the upper part of the littoral zone. Thus, 

 the same species occur in Greenland as in Iceland, although pos- 

 sibly they are not present in the same numerical proportion. But 

 one great difference exists, namely that the Greenland community 

 is found in the middle of the littoral zone, while the Iceland com- 

 munity is found much higher up. There is a similar difference in 

 the occurrence of the Porphyra; as it is found in fissures of the 

 rocks in the upper littoral zone in Greenland, while in Iceland it 

 grows upon the surface of the rocks. This difference is probably 

 due to a difference in the climate. 



It is possible that the same community (Borgesen, 12, pp. 

 716, 719) may be found at an even greater height in the Faeroes 

 than in Iceland. In the Faeroes the species are only partially 

 similar, because Monostroma groenlandicum is wholly absent, and 

 Ulothrix flacca does not seem to play such an important part there 

 as it does in Iceland. The community of filiform algae is, in all 

 probability, common along the coast of Norway (Foslie, 18; Bor- 

 gesen, 12, pp. 719— 720; Boye, 10, p. 20). 



3. The Community of Fucaceae. 



This community is the dominant one in the littoral zone and 

 comprises six associations, of which the first two, the Pelvetia- 

 association and the Fucus spiralis- association, are more closely 



