The Botany of Iceland - 01.12.1912, Page 130

116
H. JÓNSSON
which grow exclusively, or by preference, on the Fucaceæ, and tliose
which occur as frequently on other substrata and niust consequently
be considered chance visitors.
Only one single species, Polysiphonia fasligiata, is exclusively
confmed to the Fucus-belt (Fig. 7). It is well known that this species
grows only on Ascophyllum nodosum, into the frond of which it puts
its rhizoids,1 although its distribution does not coincide entirely with
that of the latter. While Ascophyllum is common everywhere along
the coast of Iceland, Polysiphonia fastigiata is common only in S.
and SW. Iceland; it has been found, also, in a single place in NW.
Iceland. Thus it keeps to the warmer parts of the sea off the coasts
of Iceland, but even within tliis area it may be absent from coasts
where the sea-water mixes abundantly with the fresh water. It did
not occur for instance at Borgarnes, nor on the nearest islands,
although Ascophyllum occurred in great quantities together with
Fucus vesiculosus and Fucus inflatus. There the sea-water is freely
mixed with water from the Iarge glacier-torrent of Hvítá in Borgar-
fjörður. Polysiphonia fastigiata does not seem able to endure such
water, but further out, along the fjord, wliere the water becomes
more saline, it grows in the ordinary manner.
Of those species which grow by preference on Fucaceœ, Ela-
chista fucicola and Ulvetta fucicola may be mentioned. The first of
these is the most important and often occurs in wonderful abun-
dance, Ulvella forms a much less important part of the vegetation,
more especially on account of its minute size.
Besides these two, otlier specics Irequently oecur which just as
often, or even more often, grow on other substrata. Of these Py-
laiella littoralis plays a very important part in tlie vegetation, espe-
cially in the spring; then it sometimes occurs in such quantities
that it almost covers large stretches of the coast. Ulothrix flacca
also frequently occurs in great abundance, as may also be the case
with Isthmoplea sphœrophora. In spring and early summer Ecto-
carpus tomenlosus and Ectocarpus fasciculatus are found growing to-
gether socially on Fucus inflatus (both of them in S. and SW. Ice-
land). Ectocarpus confervoides is also a rather frequent epiphyte. In
addition, Monostroma and Enleromorpha intestinalis inay be inentioned,
on which, again, epiphytes can grow (as for instance Chantransia-
species); also Ulothrix pseudoflacca, Acrosiphonia, Ceramium rubrum,
Ralfsia verrucosa, Conchocelis rosea, Porphyra umbilicalis and others.
1 Gertrud Tobler-Wolff, in Beiheftez. Botan. Centralbl.. Bd. 24, 2. Abt., 1909.