The Botany of Iceland - 01.12.1912, Side 154

140
H. JÓNSSON
continuous, although only as far as the substratum is favourable
for its development. By reason of the nature of the substratum,
both the upper and the lower boundaries often have an irregular
course, and stragglers froin the main body of the vegetation ofter
occur. Those Laminariaceæ which occur in the low-lying tide-pools
must be regarded as stragglers from the Laminariaceœ-community
which exists below. In the same way there are stragglers which
extend outwards into deep water, as some members of tlie com-
munity have been found at a depth of 40 metres. The community
occurs both on exposed coasts and on those which are partly ex-
posed, as well as on sheltered coasts. It is composed of perennial
species with, as a rule, strongly developed organs of altachment, a
stem-like stipe and, as a continuation of this, a lamina or leaf-Iike
portion which is originally undivided, but in some of the species,
is later divided by longitudinal slits into many lobes. The species
are the largest of all the algal species in the northern seas: thejr
grow both in pure associations and highly intermingled with one
another. The community may be said to resemble a “forest” on
the sea-bed; sometimes the “forest” is pure, sometimes mixed, and
it has its undergrowth, its “stem” epiphytes and its “leaf’ epiphytes.
The species which occur are Saccorrhiza dermatodea, Laminaria-
species and T/aria-species. Like tlie Fucaceœ-community in the lit-
toral zone, the Laminariaceæ-community is composed of a few species
of very social growth, and, just as the Fucacece-community forms the
greater part of the bulk of the vegetation in the littoral zone, so
does the Laminariaceœ-commun'úy below the limit of low-tide. If the
range of the associations diífers in depth this will be menlioned
wlien they are described.
The Associations of the Laminariaceæ Community
occur in many places in fairly regular succession from the coast
out towards the deep sea. Thus, often quite close to the coast,
Laminaria saccharina or Alaria esculenta is found occurring in very
great abundance in pure or mixed associations; beyond is found a
belt of Laminaria digilata; and deepest of all Laminaria hgperhorea.
But the order is not always so regular, and at lesser depths it is
frequently seen that the species occur socially on small areas of
the substralum, sometimes one species being dominant and some-
times another. The species maj' also occur scattered amongst one
anolher, especially at lower depths. There is a difference in the