The Botany of Iceland - 01.12.1912, Side 144

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H.JÓNSSON
greatly in size and form and may be at times considerably elon-
gated, bearing then a striking resemblance to an Enteromorpha.
Under calm conditions the inflated stage continues until the spores
at the apex of the frond are ripe.
In several places in the fjords Monostroma Grevillei var. typica
forms a luxuriant, characterizing vegetation at a depth of about
3—5 metres.
Monostroma fuscum very frequently forms associations of con-
siderable extent in the fjords at a depth of about 4 metres. The
specimens of this species which occur there are generally very large
(f. yrandis). These targe specimens are rather frequently found at
low-water mark, detached or floating at the water’s edge, and then
it may generally be taken for granted that a Monostrometum exists
further out at a depth of about 4 metres.1 Both in the fjords of
E. Iceland and in Eyjafjörður in N. Iceland this Monostrometum oc-
curred in the same characteristic manner, viz. alternating with a
Chordarietum, a Dictyosiphonetum (D. foeniculaceus), a Halosaccione-
tum, and a Rhodymenietum. Generally the order was that Rhodymenia
grew deepest (as deep as 12 metres), and M. fuscum most frequently
uppermost (at about 4 metres). Alaria and Laminaria saccharina, in
addition, may be found growúng scattered in such places, which
makes the character of the vegetation still more lieterogeneous.
Monostroma undulatum does not occur so abundantly as do the
other Monostroma species. It is found growing rather tuxuriantly,
however, in pools in the lower littoral zone, and on the stems of
Laminaria in comparatively low water.
Ulva Laduca, also, is most nearly related to this association.
This association is very common in the Færöes (cf. Börgesen,
12, pp. 731 and 764), and occurs also in Greenland (Rosenvinge, 63).
9. The Chorda-association.
This association is contposed of rather large, brown algæ. The
fronds are either non-branching, tliick fllaments (Chorda, Scytosiphon),
or else branched, as in almost all the others; one, Coilodesme, how-
ever, is almost leaf-like.
This association has an insignificant distribution, and is found
usually in patches, where the substratum is clayey or somewhat
muddy. It occurs both in the lower littoral zone above low-water
mark, and to a depth of at least 4—6 metres. The members of the
1 Strömfelt (70, p. 11) mentions this Monostrometum at Eskifjörður