MARINE ALGAL VEGETATION 



109 



coast that the smallest species (Pelvetia, Fncus spiralis) are arranged 

 in a separate uppermost belt, while the larger species are arranged 

 in belts lower down, and the largest species (f. inflatus, if the large 

 broad-fronded forms are included) occurs lowest of all. 



The Fucus spiralis-association (Fig. 4) is more luxuriantly 

 developed than the Pe/yefr'a-association and occurs just below it. On 

 flat or very gently sloping rocks this association forms a compara- 

 tively broad belt, but on a steep coast only a narrow one. Its relation 



Fig. 4. Fucus spiralis. Part of a luxuriant Fucus spi'raZf's-vegetation below the Pelvetia- 

 association. Reykjavik, Aug. 13, 1909. (From phot, by Hesselbo.) 



to exposed coasts has already been discussed. It may happen with 

 Fucus spiralis, as with Pelvetia, that it extends to so great a height 

 that at times it is not wetted daily by the sea. In such a case the 

 individuals are as a rule smaller, and are often rather strongly 

 spirally twisted; they may be found lying quite dried up on the 

 rocks, apparently without being damaged thereby. The twisting of 

 the fronds may possibly result from the drying process. 



This belt is, as a rule, somewhat sharply defined from the 

 Fucus vesiculosus-belt situated below. Although it does not always 

 happen that there is any distance worth mentioning between F. 

 spiralis and the upper outposts of the Fucus vesiculosus-association, 

 yet the boundary is almost always sufficiently distinct. 



