The Botany of Iceland - 01.12.1912, Síða 194

180
H. JÓNSSON
in ihe case of many species both the vegetative period and tlie
period of fructification is longer in the Arctic Sea and the northern
part of the Atlantic Ocean than in the remaining more southern
part of the boreal area of the same Ocean. It holds good also
for Iceland, that both tliese periods are prolonged. Iceland, the
Færöes and Greenland agree also in the fact that the summer is
richest in fruit-bearing species.
3. Littoral Winter-vegetation at Reykjavík.
The littoral vegetation changes its appearance according to the
season, and this is especially owing to the annual species. The
vegetation is most luxuriant, and ricliest in species during spring
and early summer; in the latter part of the summer the annual
species decrease in number and a quantity of tliem disappear, and
in the autumn only a small number of them is left. During winter
only a few sliort-Iived species are found, and some of them play
either no part, or only an unimportant one in the vegetation which
by that time is usually composed of perennial species. Thus, llie
number of the species of the winler-vegetation is much less than
of the summer-vegetation because the Chloroplujceœ, which is the
group in the littoral zone that is richest in species during summer,
are few in number during winter; also the number of species of
the Phœophyceœ is greatly reduced in the littoral zone during winter.
It is the Fucaceœ wlrich form by far the greater part of the mass
of plants in the littoral zone, during the winter as in the other
seasons of the year.
In December and January, in the winter 1911 —1912, the vege-
tation of the upper and lower littoral zones was composed as
follows: —
Higliest of all a Prasioletum stipitatæ occurred in patches.
Prasiola stipitata grew luxuriantly and had a normal appearance.
It was not injured by the winter climate.
Below that came a well-developed Porphyretum umbili-
calis, occurring also in patches on aecount of the surface-form
of the coast. The Porphyra was both sterile and in fruit and had
an entirely normal appearance.
Below that again came the Fncaceæ-communitv which, as is
usually the case there, consisted at the top of a Pelvetia-Fucus
spiralis-belt and at the bottom of the usual Fucus-belt (Fucus vesi-