The Botany of Iceland - 01.12.1912, Side 120

106
H. JÓN'SSON
Reykjavík, especially later in the summer, it frequently has a yel-
lowish-brown tinge.
These associations, owing to local conditions, naturally are not
found everywhere along the coasts. At tirnes they are all present,
and then generally in tlie succession here recorded; at other times
only one or another is present. Tlius, in some places, the upper
limit of the marine algal vegetation is indicated the Ulothrix-
association, and in others by tlie Bangia or the Porphgra associa-
tion; in places the entire community is absent, and then the boun-
dary is marked by Pelvetia, Facus spiratis or other Fucaceœ.
A comparison with the adjacent coasts shows that this community
is found both in Greenland and in the Færöes though it does not
behave in quite the same manner in both places. In Greenland a Mono-
stroma groentandicum -association is found which is composed of
Monostroma groenlandicum, Ulothrix flacca and Urospora mirabitis,
all intermixed with Bangia fuscopurpurea. This association occurs
in the middle part of the littoral zone. A Porphgra umbilicalis-
association occurs also in the upper part of the littoral zone. Thus,
the same species occur in Greenland as in Iceland, althougli pos-
sibly thejr are not present in the same numerical proportion. But
one great difference exists, namely that the Greenland communitjr
is found in the middle of the littoral zone, while the Iceland com-
munitjr is found much higher up. There is a similar difference in
the occurrence of the Porphgra; as it is found in fissures of the
rocks iti the upper littoral zone in Greenland, while in Iceland it
grows upon the surface of the rocks. This difference is probabljr
due to a difference in the climate.
It is possible that tlie same community (Börgesen, 12, pp.
716, 719) may he found at an even greater height in the Færöes
than in Iceland. In the Færöes the species are only partially
siinilar, because Monostroma groentandicum is wholly absent, and
Ulothrix flacca does not seem to plajr such an important part there
as it does in Iceland. The community of filiform algæ is, in all
probability, common along the coast of Norwajr (Foslie, 18; Bör-
gesen, 12, pp. 719—720; Boye, 10, p. 20).
3. The Community of Fucaceæ.
This communitjr is the dominant one in the littoral zone and
comprises six associations, of which the first two, the Pelvetia-
association and the Fucus spiratis-association, are more closeljr