The Botany of Iceland - 01.12.1912, Page 123

MARINE ALGAL VEGETATION
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coast that tlie smallest species (Pelvetia, Fucus spiralis) are arranged
in a separate uppermost belt, while the larger species are arranged
in belts lower down, and tlie largest species (f. inflatus, if the large
broad-fronded forms are included) occurs lowest of all.
The Fucus spiralis-association (Fig. 4) is more luxuriantly
developed than the Pe/ue/ia-association and occurs just below it. On
ílat or verjr gently sloping rocks lliis association forms a compara-
tively broad belt, but on a steep coast onlv a narrow one. Its relation
Fig. 4. Fucus spiralis. Part of a luxuriant Fucus spiralis-vegetation below the Pelvetia-
association. Reykjavík, Aug. 13, 1909. (From phot. by Hesselbo.)
to exposed coasts has already been discussed. It may happen with
Fucus spiralis, as with Pelvetia, that it extends to so great a height
that at times it is not wetted dailj' by the sea. In such a case the
individuals are as a rule smaller, and are often rather strongly
spirally twisted; they may be found lying quite dried up on the
rocks, apparently without being damaged thereby. The twisting of
the fronds may possibly result from the drying process.
This belt is, as a rule, somewhat sharply defined from tlie
Fucus vesiculosus-be\t situated below. Although it does not always
happen that there is any distance wortli mentioning between F.
spiralis and the upper outposts of the Fucus vésiculosus-association,
yet the boundary is almost always sufficiently distinct.