807 



In reference lo these questions opinion is divided into two 

 sharply opposing canips; the one finds the explanation in a post- 

 glacial land-bridge, which makes the immigration of the flora ap- 

 parently easy to understand. The other maintains, that this land- 

 bridge is very problematic and not necessary to explain the immi- 

 gration of the flora of the islands. 



I shall not further discuss what has already been said con- 

 cerning this question, but merely call attention to Warming's 

 treatise on this matter^ and to his paper (83) published (p. 660) 

 in this work. In the latter paper Warming again takes up the 

 discussion of this question, and on the one band emphasizes the 

 improbability of the existence of a postglacial land-bridge, on the 

 other declares that the plant-immigration may have taken place 

 by aid of the following factors: (1) hirds; (2) the wind; (3) ocean 

 currents; (4) floating ice, floating timber, etc. and finally (5) man's 

 agency. In reference to great distances, thus also to the Færoes, 

 Warming thinks that the birds, the ocean currents, and the float- 

 ing timber, etc. are of small importance or none at all. On the 

 other band he assigns great importance to the influence of the wind 

 and the agency of man. 



Shortly after this, in the spring of 1904, I published in Danish 

 my treatise on the marine alga-vegetation of the Færoes (10), in 

 which I likewise tried to explain the occurrence of the marine 

 algæ on the coasts of the Færoes by means of factors at work to 

 this day, without having recourse to the theory of the postglacial 

 land-bridge. This hypothesis was, as already mentioned in the in- 

 troduction, attacked by Porsild and Si m mons, who both adopt 

 Ostenfeld's view (64) and assume, that there has been a post- 

 glacial land-bridge by means of which the flora immigrated to the 

 islands. They maintain moreover, that as natural conditions are now, 

 the algal flora could not possibly traverse the sea; Porsild for ex- 

 ample thinks it a »physical impossibility«, that the algæ should be 

 able to cross the Gulf Stream. 



I have already replied (11) to this attack, quoting amongst other 

 arguments, several hydrographers e. g. Komm. Holm, Doc. M. Knud- 

 sen, Prof. M o h n , Prof. F r. Nansen, Kapt. Ryder, and Admiral 

 Wandel, well-acquainted with the course of the currents in the 

 North Atlantic, to prove that there is nothing to prevent floating ar- 



^ Warming, Eug. , Om Grønlands Vegetation (Meddelelser om Grønland, 

 København, 1888). 



