The Botany of Iceland - 01.12.1912, Qupperneq 143

MARINE ALGAL VEGETATION
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however, been subdivided. Reinke (58, p. 10) divides the littoral
region near Kiel into an upper zone which is always laid bare at
low-water, and a lower zone at a depth of 2—4 metres. So far as
I can judge from the species enumerated, Reinke’s upper zone
corresponds approximately with the previouslv mentioned upper
littoral zone, while the lower zone corresponds only in part with
the semi-littoral zone here described. Gran (24, p. 11) records under
the term “sublittoral vegetation” transitional formations which evi-
dently, for the most part belong to the semi-littoral communities.
On the west coast of Sweden (Kylin, 45) the border-line be-
tween the littoral and sublittoral algal vegetations is, on the coast
of Bohuslan, at a depíh of 3—4 metres, and at Halland at a depth
of about 5 metres. The upper part of the littoral zone seems to
corresjiond to some extent with tlie above-mentioned upper littoral
zone, while the lower part has something in common with the
semi-littoral zone.
Where there is no tide, the boundary between an upper and
a lower littoral zone is not, I think, so sharply defined.
8. The Monostroma-association.
This vegetation is composed of relatively large, membranaceous,
green algæ. Monostroma fnscum and M. Grevillei form associations
in a rather considerable number of places in protected localities in
the fjords, below the limit of low-tide, and to a depth of at least
4—6 metres. Tliere, tlie association is most sharply defined, although
it is fairly frequently found intermingled with other semi-littoral
associations. In the lower littoral zone also, an abundant Mono-
stroma-vegetation frequently occurs, both on a rocky substratum,
and also very often as epiphytic vegetation in other associations,
as, for example, the Halosaccion-association, tlie Corallina-association,
the Polysiphonia urceolata -association and others. In water-íilled
depressions in both the upper and lower littoral zone the Mono-
stroma species often occur abundantly.
Monostroma Greviltei var. arctica seems to belong more imme-
diately to the liltoral zone. In many places it is found entirely laid
bare, sometimes on a clayey substratum, when it often attaclies
itself to small individuals of Mytitus edulis, and sometimes wliere
the substratum of the littoral zone is pebbly. During April and Alay
this vegetation is rather characteristic, because then, the species
occurs for the greater part in the inflated stage. The bladders vary
The Botany of Iceland. I.
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