The Botany of Iceland - 01.12.1912, Blaðsíða 164

150
H. JÓNSSON
Laminariaceœ. It occurs most commonly at depths of from 6—20
metres, but has also been found as deep as 30 metres.
Many of these species grow very socially and often cover the
stipes completely, or nearly so. At Reykjavík, it is very usual in
the spring to find Laminaria hyperborea in shallow water (4—10
metres) with the stipes entirely overgrown by Rhodochorton Rothii,
Antithamnion floccosum and Polysiphonia urceolata, each on its own
particular stipe, or else intermingled. Petrocelis and Rhododermis
occur also in great abundance, almost covering entire stipes. In the
Vestmannaeyjar and at Eyrarbakki it was also a fairly common
occurrence to íind stipes of Laminaria hyperborea completely over-
grown by Dermatolithon macrocarpum. In the northern part of the
country Lithophyllum Crouani also sometimes covers the stipe of
L. hyperborea over its entire Iength. Many of the remaining species
may also occur abundantly, but most frequently the vegetation upon
the stipes is mixed, and crustaceous species grow side by side with
branching and membranaceous species.
The epiphytic vegetation seems to be most luxuriant and richest
in species at lesser depths, where the semi-littoral associations
meet the associations which extend deeper down, and where, in
addition to the Rhodophyceœ which always predominate, both brown
and green species occur. At a greater depth the species are few,
and are almost exclusively Rhodophyceœ. Generalljq the rule seems
to hold good that while the species with a more downward range
occur on the haptera or on the lower part of the stipe, the more
light-loving species occur on the upper part of the stipe; the green
algæ, however, are by no means always uppermost. Thus in the
upper portion of the Laminaria-belt Euthora, Rhodophyllis, Odon-
thalia and others frequently occur among the haptera, but in the
lower portion of the belt they may be found on the stipe almost
everywhere, especially Euthora. This agrees with Berthold’s ob-
servation of the succession of epiphytes on Cystosira in the Medi-
terranean, and with Börgesen’s observation of the order of the
epiphytes on Laminaria hyperborea in the Færöes.
The vegetation on the stipe of L. hyperborea is extremely
luxuriant in S. and SW. Iceland and is considerable both in NW.
and N. Iceland, but is poor in E. Iceland.
Epiphytes frequently occur also on the fronds of the Lami-
nariaceœ, especially in the upper portion of the Laminaria-he\t.
Here the brown algæ predominate, wliile only a few red and green