The Botany of Iceland - 01.12.1912, Síða 156

142
H. JÓNSSON
Pylaii occurs thus as a calm-water form corresponding with the
deep-water form of Alaria esculenta and with the form found on
exposed coasts. I haA7e found the Ataria Pylaii-association well de-
Aeloped in E. Iceland at a depth of 20 metres. Tlie species also
extends liigher up and may, like all the other Laminariaceœ, occur
at ahout the limit of low-tide or iu the water-filled depressions in
the lower littoral zone, hut is tlien, like tliose Laminariaceœ, of
small growth.
The Laminaria færöensis-assoeiation. The species in
question grows socially at a depth of 20—30 metres in Fossárvík
at the head of Berufjörður in E. Iceland. In its external appearance
this association exactly resembles the deep-water association of La-
minaria saccharina. The structure of the stipe differs however, be-
cause L. fœröensis has a hollow stipe like L. longicruris; as Rosen-
vinge (63, p. 211) and Börgesen (12, p. 766) point out, the air-
fdled hollow space probably serves to lift the iarge lamina from
the sea-bottom.
In deeper water, L. fœröensis occurs in the same manner in the
Færöes as it does in E. Iceland (Börgesen, loc. cit., p. 766), but
differs somewhat in shallow water. In Greenland and Iceland, as
in the Færöes, the hollow-stemmed Laminariœ prefer protected
localities.
The Alaria esculenta-association. This is distributed
very commonly along all the coasts of Iceiand. It prefers a rocky
substratum, but may occur also on pebbles as Laminaria saccharina
occurs, and frequently in company with it. As a rule, the associa-
tion is best developed at a deptli of 6—16 metres; but the species
occurs, in addition, growing socially at a depth of 3—4 metres and
again, sometimes as deep as 30 metres. Tlie association is pure or
only sliglitly mixed, and then usually with L. saccliarina, L. digitata
or Al. Pylaii: it often stretches for miles in the fjords. The species
(Ataria esculenta) varies in a manner somewhat similar to the varia-
tions of Laminaria saccharina and L. digitata. In very exposed places,
there is found in sliallow water a narrower-fronded form with nar-
row, ieathery sporophylls. This form cannot be termed a surf-form
like L. digitata f. stenophylla but it may, however, merit the title of
an exposure-form. Another form, which is much larger, both as
regards the length and l)readth of its fronds, occurs in deeper water