236 VEGETABLE COLONIZATION. 



new problem presented itself: Did these vegetable colonies come from 

 Europe or America ? A great number of plants being common to 

 both the Old and New World, the question presented some difficulties. 

 I found, however, more than a hundred species exclusively European; 

 all the others were common to Europe and America. Europe, then, 

 must have had the greater share in the colonization of these archipe- 

 lagoes ; a great vegetable migration had advanced across England and 

 Scotland, the Orkney, Shetland, and Faroe islands, as far as Iceland. 

 Some species had come directly from the coasts of Norway. But, in 

 the mean time, in an opposite direction, the Arctic plants (natives of 

 Greenland) had propagated themselves across Iceland, Faroe, and 

 Shetland, to the mountains of Scotland, where they found a second 

 home. This double migration is evident from the proportional number 

 of the different plants ; for if we calculate that of exclusively European 

 plants which enter into the flora of Shetland, we find it to be a fourth, 

 that of Faroe but a seventh, and, finally, that of Iceland but a tenth. 

 Thus, as we leave Europe behind us, the number of plants of its 

 peculiar growth proportionably diminishes ; but, at the same time, 

 that of the plants of Greenland origin increases in very nearly an 

 inverse ratio. 



Though entirely agreeing with Mr, Forbes as to the fact of the 

 colonization of the isles of the northern Atlantic, I hesitate before 

 adopting his bold and novel hypotheses. Without interrogating the 

 remote past, I find in the action of existing causes a plausible explana- 

 tion of the transportation of seeds from a continent to the nearest 

 islands, and from one island to another, from England as far as Ice- 

 land. 



A great current (the gulf stream) takes its source in the Gulf of 

 Mexico^ follows the coast of America as high as Newfoundland, and 

 then traversing the Atlantic bathes the western shores of Scotland. 

 It is this which conveys thither the seeds of Mexico, still retaining 

 their germinative faculty ; it is this which has cast on the shores of 

 the Hebrides the Eriocaulon septangulare, a species belonging to North 

 America, and the only one of the British plants which is not also 

 European. In coasting the shores of Scotland the gulf stream collects, 

 doubtless^ the innumerable seeds which the water courses bear into the 

 sea, carries them northward with it, and strews them along the friths 

 and shallows of Shetland, Faroe^ and Iceland. This current appears 

 to me the principal agent in disseminating the plants of Europe 

 among these islands, and hence the predominance of the European 

 flora over that of North America. 



The winds, those aerial streams, play their part also in the diffusion of 

 species, but, like that of the marine currents, it evades all direct ob- 

 servation. Whoever has once experienced those long and terrible 

 storms of wind which sweep the northern seas can hardly doubt their 

 efficiency in transporting from one island to another light seeds, often 

 furnished with down and membranes, which facilitate their suspension 

 in the air. A recent fact gives additional force to this conjecture. 

 The 2d September, 1845, at nine in the morning, there was an erup- 

 tion of Hecla in Iceland. On the 3d, cinders fell in the most southern 

 of the Faroes, and the same day were wafted to Shetland, the Ork- 



