The Botany of Iceland - 01.12.1912, Blaðsíða 162

148
H. JÓNSSON
mates to surf. In deep water the Laminaria fronds will always
moderate the motion.
In shallow water, especially where the bottom can be seen, it
is easy to observe the under-vegetation, but in deep water one has
to rely upon the specimens brought up by the dredge.
The under-vegetation is not divided according to the various
associations of the npper vegetation, bnt seems to possess the same
character wherever it is observed. In S. Iceland (the Vestmannaeyjar
and Eyrarbakki) Phijmatolithon polymorphum occurs in great abun-
dance, covering the bottom entirely for large distances near the
coast as an undergrowth. It is mainly composed of crustaceous,
membranaceous, and more or less branching Florideœ.
A. Crustaceous Algæ. In several places in N. and E. Iceland
I found a luxuriant under-vegetation formed of Lithothamnion lœve,
L. circumscriptum and L. glaciale. Among these species the first men-
tioned especially seemed to be widely distributed bolh on the bottonr
of an Alaria and a Laminaria association. In E. Iceland Lithothamnion
flavescens and L. foecundum in addition, like Clathromorphum compac-
tum, were very frequent on a Laminaria-association-bottom. Together
with tliese species occurred Peyssonetlia Rosenvingii, Cruoria arctica,
Lithoderma and others, as in the crustaceous algal vegetation (see p. 155).
B. Membranaceous and Branching filamentous spe-
cies. The upper layer, with which are also associated inter-
mingled species, varies considerably according to the depth. In
addition to a number of the species which extend further down-
wards, various semi-littoral species may thus occur in the upper
part of the Laminaria-belt. A number of the species which grow
on the Laminaria stems may also occur on the bottom between
tlie Laminariœ.
Here it is really a question of several associations; the lowest
layer, as mentioned, is the crustaceous alga-association; the second
layer is composed in its upper part of semi-littoral associations,
which meet the associations w^hich extend deeper and are mainly
associations of Rhodophyceœ-, and the uppermost layer is the Lami-
naria-association. The species are named w'here these associations
are mentioned, and are thereíbre omitted here.
The Epiphyte-vegetation. Epiphytes very frequently occur
on the stipes and laminæ of the Laminariaceœ, and it is a parti-
cularly common occurrence for old stems of Laminaria hyperborea
to be entirely overgrown, for the epiphytic vegetation is much more