MARINE ALGAL VEGETATION 145 



mediate forms, so are the various associations connected. If the 

 deep-water character of the association is taken as a starting point, 

 we notice that it changes gradually with decreasing depths on ex- 

 posed coasts, and that somewhere near the limit of low-tide it 

 assumes an entirely different character, which is displayed in the 

 leathery, long-stemmed form with a narrow and slightty-divided 

 frond (f. stenophyllaj. On an exposed coast this variety might be 

 termed the shallow-water type or perhaps, rather, the surf-type, in 

 conformity with the surf-form of Fucus inflatus. The surf-character 

 was very beautifully and typically developed in the Vestmannaeyjar ; 

 here /'. stenophylla grew very socially, forming a continuous belt, 

 the upper boundary of w r hich occurred almost at the limit of low- 

 tide. When during low-tide the waves receded it was very inter- 

 esting to see how easily the leather}', narrow, slightly-divided laminae 

 moved with the waves, and everywhere, as far as the waves receded, 

 the rocky substratum between the Sfenojo/jy/Za-individuals was quite 

 reddish in colour from the encrusting Phymatolithon polymorphism. 

 The Laminaria plants were very firmly attached to the rock — a 

 fact evidently well known to the fishermen, as they fastened the 

 boat to a Laminaria while we went ashore. The stipe is leathery 

 and pliable, and the plants cling closely to the substratum when 

 the waves recede. 



I have found /'. stenophylla in other places, although not in 

 such abundance, and not quite so typical. Here the same rule 

 applies as with regard to Fucus inflatus and Laminaria saccharina, 

 that the tendency to vary seems to depend on the greater or lesser 

 movement of the water; on coasts which are somewhat exposed, a 

 Laminaria dighata-association is rather frequently found at about 

 the limit of low-tide, with a character midway between the surf- 

 character and the deep-water character. 



If we again take the deep-water character of the association as 

 a starting point, and move inwards towards the protected coasts, 

 we see that the character changes again, but in another direction. 

 The stipe becomes shorter and the frond much broader and slit 

 into fewer and broader lobes. Within the fjords, in W. and E. Ice- 

 land especially, the character is entirely different from the deep- 

 water character. Here occur forms with verj r broad fronds which 

 are either undivided or divided into two, or a few, very broad 

 lobes (f. cucullata). Generally the depth is about 4 — 20 metres, even 

 deeper occasionally. I have found associations with this character 



The Botany of Iceland. I. \Q 



I 



