The Botany of Iceland - 01.12.1912, Page 127

MARlNE ALfiAL VEóE'fA'ffON
113
Generally this species forms a pure association, but yet, some-
tinies, it and Ascophqllum can grow intermixed.1 It is always sub-
merged at high-water, but seems well able to withstand desiccation
at low-water, when however the upper side of the frond dries up
considerably, especially on rocks which face the sun, and may then
— and this is true of Fucus inflatus also — be bent upwards, or
even slightly distorted, at the apex, though never to the same extent as
is the case with Fucus spiralis. When such a branch is lifted up,
it can be seen that the under side is moist, even on a warm sum-
mer’s day. During low-tide the Fucus plants lie prostrate on the rock,
one plant overlying the other, or one branch of the frond covering
the other, and in this way some water is retained amongst the plants.
Naturally, this applies also to the members of the other asso-
ciations in the í’iicus-belt. Those individuals which liang freely from
the rocks are exposed more tlian others to desiccation.
The Ascophyllum-association diífers from the other asso-
ciations in its light-brown colour, and, in addition, by the occur-
rence of Polysiphonia fastigiata, wliich grows very luxuriantly on
it in S. and SW. Iceland; it is often somewhat singular to see the
light-yellow Ascophijltum-beU with the numerous dark reddish-hrown
patches of Polysiphonia.
So far as the behaviour of the species during exposure to the
beat of the waves is concerned I must refer to the above-mentioned
remarks, and can only add that at times it may also occur in the
most exposed places, but no longer in the uppermost belt. Here
it gives place to the surf-forms of Fucus inflatus (f. exposita, f. den-
droides), which form a narrow belt at the upper boundary of the
Fucus-he\[. Ascophyltnm occurs, then, between this and the real Fucus
inflalns-he\t, which retains its usual position. In a few places, how-
ever, on the most exposed poinls, Fucus inflatus only is found.
The Fucus inflatus-association. When exposed, this spe-
cies behaves conversely to Fucus vesiculosus and grows most luxu-
riantly on exposed coasts. Thus, it behaves in Iceland as it does
in Greenland (Rosenvinge, 63) and in the Færöes (Börgesen,
12). In Iceland, as in other places, the species varies extremely
and must be considered very capable of adapting itself to varying
circumstances, especially as regards exposure. The association can
— in accordance with the exposure — be divided into three belts: —
The Surf-belt, the Wave-belt, and the Calm-belt.
1 The epiphyte-vegetation is mentioned subsequently.
The Botany of Iceland. I.
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