The Botany of Iceland - 01.12.1912, Blaðsíða 134

120
H. JÓNSSON
ln addition Ceramieta formed by Ccramium rubrum, and Cal-
lithamnioneta formed by Callithamnion Arbuscula, occur distri-
buted in patches, especially in the Vestmannaeyjar.
The following species, growing in a more scattered manner,
occur also in the under-vegetation of the Fucus-he\t: —
Delesseria alata. Plumaria elegans.
Lithothamnia.
The species of the under-vegetation thus belong principally to
the red algæ; only two species being brown, one blue-green and
one being a lichen. The majority of the species belong to the shade-
vegetation of the littoral zone.
4. The Enteromorpha-association.
Of the Enteromorpha-species E. intestinalis is the most common
and the most variable. The variability, no doubt, principally de-
pends upon local conditions, possibly also, on the age of the species.
The typical form is extremely common in the upper littoral zone,
but occurs most luxuriantly in the water-filled depressions. As a
rule, the plants have a social growth, although they rarely cover
large areas. E. protifera and E. ctathrata, on the other hand, occur
in such abundance tliat it might be justifiable to speak of an asso-
ciation forrned of branching Enteromorphas. These species are found
in greatest abundance in the middle littora! zone, often in empty
depressions in the lower part of the Fucus-belt proper, and may
sometimes extend !>eyond the boundary of the lower littoral zone,
where they then encounter semi-littoral associations, for example,
Dictyosiphonetum, Chordarietum and others. While the typical form
of E. intestinatis seems to flourish during the spring, the branching
forms E. prolifera and E. clathrala are noticeable in the summer.
I have known these two species to occur predominantly in June,
July and August on the same substratum upon which Urospora
Wormskioldii was growing in great quantities in the month of May.
Enteromorpha Linza is also a summer species, and, although
it forms in several places pure Enteromorpheta of lesser extent, plays
only an inferior röle in the Enteromorpha-association.
In E. Iceland, on the point between SeydisQörður and Loðmundar-
fjörður, at the height of the lower part of the Fucus-belt and a
Iittle lower, I found a Chlorophycece-vegetation which must be con-
sidered to belong most nearly to this association. A Monostro-