The Botany of Iceland - 01.12.1912, Síða 72

58
H. JÓNSSON
Skagafjörður; while Cystoclonium, Polysiphonia nigrescens and Leathesia
do not extend further than the most western part of tlie nortli
coast (the small fjords in Húnaflói). Only Delesseria sanguinea now
remains; strictly speaking, this appears to belong to the south and
south-west coast, but has on one occasion been found in E. Iceland,
cast up on the shore. It did not appear to have coine from a
distance, and it probably grows there, though I did not come across
it in the dredgings.
Thus all these 53 species liave on the whole a southern and
western distribution in Iceland.
The above shows that there is a large neutral territory where
the species with a south-western and those with a north-eastej-n
distribution meet and intermingle. This boundary area comprises
almost the whole of the north coast, the north-west fjords and, to
a certain extent, the northern part of the soutli-west of the country.
(For further details see below under the Floristic Boundaries.)
THE COMPONENTS OF THE ALGAL FLORA.
At present 200 species of Marine Algæ are known from Iceland.
In tlie plant-geographical groups establislied by Börgesen and my-
self (Börgesen and Jónsson, 14) these are distributed in the
following manner. The deíinition of the groups is here reproduced
almost literally from the publication mentioned.
A. The Arctic Group.
The species of this group belong to the arctic area of the sea.
The southern limit of tliis area extends from the north and east of
Norway southward to the south-east point of Iceland, where tlie
boundary is sharply defined. From E. Iceland the boundary line
extends to the nortli of Iceland between Iceland and Greenland,
and then turns considerably southward to the North Atlantic coast
of America. The flora of the boreal area of the Atlantic passes
without any distinct Iimit into the arctic algal flora on both sides
of the Atlantic. In Iceland the limit is distinct only at the south-
east point whereas the boundary is very indistinct on the north-
east part of the coast.
Some of the species of this group occur, but only rarely,
south of the border-zone.