The Botany of Iceland - 01.12.1912, Side 43

MARINE ALGAL VEGETATION
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this réspect, however, tliose 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 Rosenvinge (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 Færöes, as Börgesen
(11 and 12) sets the limit far above liighest 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 algæ can
be found rather high up, and if tlie 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 tliat it
washes over them, and we no longer think it strange that they
grow in so high a position. While the inarine algal vegetation, as
mentioned hefore, 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 tlie vegetation; marine algæ,
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-
senvinge 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 towrards the
land, are treated collectively. The volume of water which is driven
towards the coast by a sea-wind raises the water-level. While the
tidal wTave rises, the sea moved by the wind works together with