ICONGL. SV. VET. AKADEMIENS HANDLINGAK. BAND 20. JSr:0 5. 



77 



are of such a kind. The other families which are represented in the Flora of Scan- 

 dinavia by only one species, are richer in species farther to the South, and may there- 

 fore be supposed to have immigrated into the Scandinavian Flora from that direction. 

 Table IV shows that the majority (54) of the 90 (92?) genera of the arctic Flora 

 are represented by only one species; the greatest number of species possessed by any 

 genus is 9 (Laminaria), and there are only few genera with any considerable number 

 of species. Thus the average number of species in each genus becomes small, namely 

 1,9. This is less than in the Flora of Scandinavia (2,3), of New-England (2,i), of Great 

 Britain (3,5), of Cherbourg (2,4), and even less than in the Flora of the Norwegian 

 Polar Sea (about 2,o). Among the genera of the arctic Flora the following are mono- 

 typical: Polyides, Hcemescharia, Hydrolapathum, Dumontia, Furcellaria, Haplospora, Di- 

 chloria, Isthrnoplea, Gleothamnion, Diplonema, and Bulbocoleon; two of these are unknown 

 without the arctic region. These circumstances, viz. the little number of species in the 

 genera and the richness in monotypical genera, tend to prove the high age of the re- 

 gion of the arctic Flora. 



The following species of the arctic Flora are common to all the three provinces 

 of the region: 



Odonthalia dentata, 

 Rhodomela lycopodioides, 

 Polysiphonia arctica, 

 Delesseria sinuosa, 

 Sarcophyllis arctica, 

 Halosaccion ramentacewn, 

 Phyllopliora inter rupta, 

 Ahnfeltia plicata, 

 Fucus evanescens, 

 Laminaria solidungula. 



Laminaria cuneifolia (?), 



» nigripes, 



Chordaria flagelliformis, 

 Elachista fucicola, 

 Lithoderma fatiscens, 

 CkcBtopteris plumosa, 

 Sphacelaria arctica, 

 Pylaiella lituralis, 

 Enteromorpha micrococca, 

 Rhizoclonium pachydermum. 



Accordingly 19 or possibly 20 species, i. e. about 10 % of the total number of 

 species in the whole region, about 15 % of that of the province of Spitzbergen, 70 % 

 of that of the Siberian province, and about 16 % of that of the American province. 

 A survey of the relation of the provinces to each other, with regard to the number of 

 species, is exhibited in the following table. 



