The Botany of Iceland - 01.12.1912, Side 158

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H. JÓNSSON
about the limit of low-tide, down to a depth of about 30 metres.
Small individuals may be found in the lowermost water-filled de-
pressions of the littoral zone. Compared with the other commonly
distributed Laminaria-species, L. digitata and L. ligperborea, then L.
saccharina generally keeps nearest to the coast, especially the more
leathery, shallow-water form. In shallow depths the succession can
be perceived distinctly, but with regard to greater depths conclu-
sions must be drawn from what is brought up by the dredge. The
succession usually is, that while L. saccharina keeps nearest to the
Iand L. hyperborea extends deepest.
As is well known the species varies very much, according to
the depth and the degree of exposure. A form with leathery, thick
fronds with a rough surface occurs near land on somewhat ex-
posed coasts in those depths where the eífect of the beat of the
waves is distinctly observable. At greater depths another form oc-
curs, the deep-water form, with long, broad and comparatively thin
fronds; and in protected localities inside the fjords of E. and W.
Iceland a third form occurs at a depth of 4—20 metres. This form
(f. latifotia) is long-stemmed, with comparatively very broad lamina
and an entirely smooth surface. As each of these forms grows very
socially the character of the association varies in accordance with
the depth and the exposure.
The Laminaria digitata-association. This association is
very common everywhere along the coasts where there is a rocky
substratum, from a depth of about 4 to about 25 metres. On rocky
coasts, however, small specimens occur just at the limit of low-tide,
and there represent a kind of boundary. Small individuals may
occur also in water-filled depressions in the lowest part of the
littoral zone.
The tendency of Laminaria digitata is to vary in the same
manner as L. saccharina, and thus the character of the association
differs according to the depth and the degree of exposure, as the
forms, individually, grow socially. The typical appearance of the
association is determined by the deep-water form, or the typical
form, which seems to grow most luxuriantly at a depth of about
10—20 metres. Here the species attains its greatest length and, as
a rule, the stipe is so strong that it is able to raise the much-
divided lamina from the bottom.
Just as the forms are connected with one another by inter-