KONGL. SV. VET. AKADEMIENS HÄNDLINGAK. BAND. 20. N:<> 5. 61 



they show that sea-regions belonging to the area of the same sea-ciirrents do not 

 always possess an essentially similar vegetation, and that one must not accordingly, wheii 

 attempting to divide the marine Flora into different geographical regions, fix the limits 

 of these in all seas chiefiy according to the sea-currents ^). There may be found external 

 conditions opposing insurmountable obstacles to the leveling tendencies of the currents 

 and keeping regions isolated from each other, whose vegetations sea-currents are ever 

 striving to level and to assimilate. The circumstances which counteract and annihilate 

 the action of the Gulf Stream and which have therewith maintained the marine Flora 

 of Spitzbergen at such a high degree of diflference to that of the Norwegian Polar Sea, 

 I consider to be chiefly the unsuitableness of the litoral zone of Spitzbergen for a richer 

 vegetation, the low temperature of the water, and the insufficiency of the light. Most 

 of the alga3 on the arctic coast of Norway belong to the litoral zone, and apparently 

 it is chiefly algx of this kind that may be expected to be transported to Spitzbergen 

 by the Gulf Stream and such objects as are carried by it towards the North. When 

 they have arrived at Spitzbergen, they cannot thrive or spread there in their wonted 

 places. The bottom is unfit for them, the ice destroys them, the temperature of the 

 water is too low for them, and the layers of air with which they are brought in con- 

 tact during ebb-tide, are often so cold as to injure the algte, stopping their development 

 and diminishing their power of resistance. The temperature of the water in the sub- 

 litoral region is at or below 0° during the whole year, accordingly very much lower 

 than that to which on the coast of Norway they are exposed in the coldest season. 

 How could these Norwegian species, which love light and are accustomed to it, be 

 expected to live here in darkness or dimness during a great part of the year, enjoying 

 even during the rest of the year, on account of the different place where they grow, 

 a less quantity of light than in those regions from where they have come? What has 

 been said here of the Flora of Spitzbergen, holds good essentially even of the Flora 

 of the eastern Murman Sea. 



Thus the out-lines of the history of the arctic marine Flora, as based on the 

 results of the preceding investigation, may be stated as follows. The Flora has had 

 its centre of development in the Arctic Sea. Its area was more extensive during the 

 glacial period than at present. It has been recruited in låter times by more southern 

 species. The immigration has been larger into certain parts of the Arctic Sea than 

 into others; in the Norwegian Polar Sea it has been so large that the Flora has here 

 löst its arctic character; in other parts it has, on the contrary, been much smaller 

 than might be expected on account of the currents prevailing, which are highly favour- 

 able for an immigration from more southern seas. 



') Cp. J. G. Agakdh, Spetsb. Alg. Progr. p. 1. 



