66. KJELLMAN, THE ALGZ OF THE ARCTIC SEA. 
Thus the whole augmentation gained by the Flora on the arctic coast of Norway 
during the last part of the glacial period, and after its end, would amount to about 
128 species, i. e., about 66 per cent of the total number of its species, as known at 
present. 
The majority of these have surely immigrated from the south. But such a sup- 
position cannot be made with regard to all. The last-mentioned 9 species must be 
excluded from it as well as the following ones, which, as far is hitherto known, are 
peculiar to the Norwegian Polar Sea, namely, 
Lithothamnion soriferum, Monostroma undulatum, 
» alcicorne, Monostroma cylindraceum, 
» intermedium, » saccodeum, 
Polysiphonia Schitbelerii, » angicava, 
Diploderma amplissimum, » arcticum, 
Lithoderma lignicola, » crispatum, 
Pylaiella nana, Chxtomorpha septemtrionalis, 
Chetophora pellicula, Ulothrix Sphacelariz. 
There is at present no other way of explaining the occurrence ofthese species 
than to assume that they have developed themselves within the Norwegian Polar Sea. 
The law for the development of new forms being that one type is originally varied, 
not that new types are formed, the fact of so many of these species being modifications 
of two generic types, which are, besides, rich in other forms within the Norwegian 
Polar Sea, may be said to speak for the hypothesis that many of these species, if not 
all, have had their centre of development in the region where they grow now. It 
should be remarked too, that Polysiphonia Schiibelertt and Lithoderma lignicola are nearly 
related to other species occurring in the Norwegian Polar Sea, the former to Polyst- 
phona fibrillosa, the latter to Lithoderma fatiscens. This is the case even with many 
of the nine first-mentioned species. Phyllophora Brodiwi is hardly anything else than 
a southern form of Phyllophora interrupta, Alaria Pylaw is very closely allied to Alaria 
membranacea, and Antithamnion floccosum and A. Pylaisei, as has already been intimated 
and will be shown in detail below, may be regarded as species developed out of Anti- 
thamnion boreale, commonly distributed in the Arctic Sea. The above-mentioned species 
of Fucus constitute a pretty closely connected series, and there may be shown reasons 
why this series should possibly be considered as having issued from the arctic Mucus 
evanescens. But the change of the Flora of the Norwegian Polar Sea did not stop at 
the expulsion of old species, the immigration of new ones, and the development of 
new forms; even the general character of the vegetation has altered in an essential 
degree. With regard to the distribution of the species, this Flora differs, as has been 
shown before, from that of other parts of the Arctic Sea, by the predominating species 
being different. I have mentioned above, which species are to be regarded as charac- 
teristic of the Norwegian Polar Sea, i. e., are most commonly disseminated, occur in 
the greatest numbers, and contribute most to stamp the vegetation with a peculiar 
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