The Botany of Iceland - 01.12.1912, Blaðsíða 183

MARINE ALGAL VEGETATION
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in the following, name some species which I am fairly'Certain may
be included among the perennials: —
Halosaccion ramentaceum.
Polysiphonia urceolata.
Rhodomela lycopodioides.
Odonthalia dentata.
Ptilota plumosa.
Rhodochorton Rothii.
Gigartina mamillosa.
Ahnfeltia plicata.
Euthora cristata.
Rhodophyllis dichotoma.
Rhodymenia palmata (?).
The crustaceous algæ sucli as Hildenbrandia, Petrocelis, Cruoria,
Peyssonellia and Rhododermis, and by far the greater number of the
calcareous algæ must also be classed as perennial.
2. Periodical Changes.
The Period of Activity. The Period of Rest. The period
of activily of tlie annual species is identical with their period of
life and it extends, probably as regards the majority of the species,
over the spring and summer months. The perennial species and
the species which can live more than one year, have a very long
period of activity which extends over the greater part of the year
with the exception of the darkest part; consequently these species
have a very short period of rest. Although from the observations
to hand it is not possible to fix the length of the period of rest,
yet they indicate that it must be short. The Fucaceœ may be men-
tioned as an examiile. Their vegetative growth appears to be very
slight during December—January, and in the case of llie older
individuals there is probably none at all at that time; but although
tlie majority of the individuals of the Fucacea’ are sterile during
winter yet, even in December, reproductive organs are developing
liere and there. Young planls of the summer or autumn appear to
have vegetative growth also during the winter. In the Fucaceœ-belt,
taken as a whole, the period of rest is consequently extremely short.
In the sublittoral zone I think that entire rest must be of extremely
short duration.
Renewal of the lamina. The young shoots. As is well
known, a renewal of the lamina takes place yearly in the Laminaria-
species. At what time this takes place in Iceland cannot be stated
with absolute certainty, but the observations seem to indicate tliat
the new lamina begins to grow even in the winter time, as tlie light
increases. I believe that in SW. Iceland a general renewal of the