MARINE ALGAL VEGETATION 107 



connected with each other than they are with the remaining asso- 

 ciations, which also are mutually very closely connected. In this 

 way the community may be divided into two belts, of which the 

 first comprises the two first-mentioned associations, and the second 

 the remaining four. The Peluetia- Fucus -spiralis-beli is narrow. It 

 is situated in the upper part of the littoral zone, at, and just below, 

 lowest high-water mark, i. e. flood-mark at neap-tide. It has only 

 one layer of vegetation, as there is no undergrowth worth men- 

 tioning, and it is entirely devoid of epiphytes; it is submerged in 

 normal conditions for a very short time. 



The second, the Fucus-he\t is broad; it occurs in the lower part 

 of the upper littoral zone, just above low-water mark of neap-tide. 

 The vegetation occurs in two, and sometimes in three, layers and 

 epiphytes are present in abundance. The vegetation is submerged 

 much longer than in the first belt. Thus, these two belts differ so 

 greatly that they cannot be treated together. 



The Pelvetia-Fucus-spiralis-belt. 



This belt is of common occurrence, and its vegetation is luxuriant 

 in S. and SW. Iceland, but in the other parts of the country is 

 sparse and devoid of Pelvetia. This belt is not continuous except 

 along short distances, and its vertical height is inconsiderable; but 

 the breadth may sometimes be fairly considerable, especially on 

 very gently sloping coasts. It grows on rocky coasts, and in places 

 where these consist of a talus of debris the vegetation is distributed 

 in patches which is a natural consequence of the surface, the limit 

 of the association being rather sharply defined downwards. Pelyetia 

 and Fucus spiralis do not grow intermixed, but occur in two pure 

 and distinct associations. They grow luxuriantly on exposed coasts; 

 in the most exposed parts of the ( coast, however, they seem to 

 recede. Thus, this belt was either absent from, or was poorly re- 

 presented on the most exposed points at the extremity of Snrefellsnes 

 and of the Vestmannaeyjar and at the extreme end of Reydarfjordur; 

 but there occurred in its place surf-forms of Fucus inflates (f. e.r- 

 posita and f. dendroides). 



The Pelvetia -association (Fig. 3) always occurs highest of all. 

 As already mentioned it is found in S. and SW. Iceland only, but 

 there it occurs in great abundance in many places; in some places its 

 vegetation is poor, and sometimes only a few scattered individuals 

 are found. This is more particularly the case in places where Pelvetia 



