142 H. JONSSON 



Pylaii occurs thus as a calm-water form corresponding with the 

 deep-water form of Alaria escalenta and with the form found on 

 exposed coasts. I have found the Alaria Pf//azz-association well de- 

 veloped in E. Iceland at a depth of 20 metres. The species also 

 extends higher up and may, like all the other Laminariacece, occur 

 at about the limit of low-tide or in the water-filled depressions in 

 the lower littoral zone, but is then, like those Laminariacece, of 

 small growth. 



The Laminaria fseroensis-association. The species in 

 question grows socially at a depth of 20 30 metres in Fossarvik 

 at the head of Berufjor5ur in E. Iceland. In its external appearance 

 this association exactly resembles the deep-water association of La- 

 minaria saccharina. The structure of the stipe differs however, be- 

 cause L. f&roensis has a hollow stipe like L. longicruris ; as Rosen- 

 vinge (63, p. 211) and Borgesen (12, p. 766) point out, the air- 

 filled hollow space probably serves to lift the large lamina from 

 the sea-bottom. 



In deeper water, L. fceroensis occurs in the same manner in the 

 Faeroes as it does in E. Iceland (Borgesen, loc. cit., p. 766), but 

 differs somewhat in shallow water. In Greenland and Iceland, as 

 in the Faeroes, the hollow-stemmed Laminaria* prefer protected 

 localities. 



The Alaria esculenta-association. This is distributed 

 very commonly along all the coasts of Iceland. It prefers a rocky 

 substratum, but may occur also on pebbles as Laminaria saccharina 

 occurs, and frequently in company with it. As a rule, the associa- 

 tion is best developed at a depth of 6 16 metres; but the species 

 occurs, in addition, growing socially at a depth of 3 4 metres and 

 again, sometimes as deep as 30 metres. The association is pure or 

 only slightly mixed, and then usually with L. saccharina, L. digitata 

 or ALPylaii; it often stretches for miles in the fjords. The species 

 (Alaria esculenta) varies in a manner somewhat similar to the varia- 

 tions of Laminaria saccharina and L. digitata. In very exposed places, 

 there is found in shallow water a narrower-fronded form with nar- 

 row, leathery sporophylls. This form cannot be termed a surf-form 

 like L. digitata f. stenophylla but it may, however, merit the title of 

 an exposure-form. Another form, which is much larger, both as 

 regards the length and breadth of its fronds, occurs in deeper water 



