66 KJELLMAN, THE ALG^ 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 foUowing 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 Schtibelerii, » angicava, 



Diplodei'ma amplissimum, » arcticum, 



Lithoderma lignicola, » crispatum, 



Pylaiella nana, Cha^tomorpha septemtrionalis, 



Chajtophora pellicula, Ulothrix Sphacelaria3. 



There is at present no other way of explaining the occurrence of these species 

 than to assume that they have developed themselves within the Norwegian Polar Sea. 

 The law for the development of new forras 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 h'e 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 Schubelerii and Lithoderma lignicola are nearly 

 related to other species occurring in the Norwegian Polar Sea, the former to Polysi- 

 phonia Jibrillosa, the latter to Lithoderma fatiscens. This is the case even with many 

 of the nine first-mentioned species. Phyllopjhora Brodioii is hardly anything else than 

 a Southern form of Phyllophora interrupta, Älaria Pylaii is very closely allied to Älaria 

 membranucea, and Äntithamnion Jloccosuin and A. Pylaism, as has already been intimated 

 and will be shown in detail below, may be regarded as species developed out of Änti- 

 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 Fucus 

 evanescens. But the change of the Floi'a 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 



