MARINE ALGAL VEGETATION 29 



this respect, however, those species should be excepted which can 

 grow both in salt and in fresh water, as for example, Enteromorpha 

 intestinalis (the principal form) and others. Naturally, such species 

 cannot be taken into account when defining the upper limit of 

 growth of marine algal vegetation. 



If we compare the upper limit of the marine algal vegetation 

 in Iceland with the same limit in Greenland it appears that they 

 agree almost completely, as Rosen vinge (63, p. 89) sets the limit 

 in Greenland almost at flood-mark at neap-tide. On the other hand 

 there seems to be an incongruity with the Faeroes, as Borgesen 

 (11 and 12) sets the limit far above highest flood-mark in exposed 

 places and almost at uppermost flood-mark in sheltered places. 



If we institute comparisons with more distant coasts, for instance 

 with the west coast of Sweden, the algal vegetation of which has 

 lately been described by Kylin (43), we find that, as regards the 

 upper limit, the case is the same as in Iceland, that is, the upper 

 limit is coincident with an average water-level which lies higher in 

 exposed places than in sheltered ones. 



In Iceland, indeed, on a very exposed coast, marine algae can 

 be found rather high up, and if the sea is smooth and calm they 

 may appear to be rather far away from the water; but on returning 

 to the same place when the sea is in motion we see that it 

 washes over them, and \ve no longer think it strange that they 

 grow in so high a position. While the marine algal vegetation, as 

 mentioned before, only extends upwards to an average water-level, 

 it frequently happens on flat coasts that the land-vegetation is sub- 

 merged at spring-tide. This occurs both in the interior of the fjords 

 and on the lower islands, and may generally be distinguished by 

 the appearance and the components of the vegetation ; marine algae, 

 however, do not occur among such vegetation. 



Some phanerogams, e. g. Atriplex, Mertensia, Cakile, etc., also 

 grow below the upper limit of the littoral zone. According to Ro- 

 sen vinge it happens in Greenland also that the land- vegetation is 

 submerged at spring-tide. 



b. The Swell. Here, those inequalities in the surface of the 

 ocean which in every -day language are called waves, and that 

 volume of water which, with a sea-wind is forced in towards the 

 land, are treated collectively. The volume of \vater which is driven 

 towards the coast by a sea- wind raises the water-level. While the 

 tidal wave rises, the sea moved by the wind works together with 



