DISTRIBUTION OF PLANTS IN BRITAIN. 589 



ranean regions to the British islands, the plants of the Asturias, and 

 those of Armorica, peopled the south of England and Ireland. To 

 this period succeeded the glacial epoch, during which the lands were 

 immerged to a depth of about 1300 or 1400 feet. This is the period 

 of the migration of the arctic plants, which still inhabit the tops of the 

 Scottish mountains. When these lands emerged anew, England was 

 united to France, the temperature being such as it is at present. At 

 this time, the great German floral invasion took place, absorbing, so to 

 speak, all the rest, and leaving very slight remains of them. Thus, 

 Avhile the Asturian plants, those of the south, are reduced to a small 

 number of species confined to the south-west of Ireland, the hardy 

 vegetables of the north completed their conquest. The colonization 

 being completed, England became separated from the continent. 



1167. Martins agrees with Watson and Forbes in their general 

 views of the British flora, adopting the following types : 



1. Asturian Type the remains of a Peninsular flora. 



2. Armorican Type vegetation like that of Brittany and Normandy. 



3. Boreal Type flora like that of the Swiss Alps, Lapland, Iceland, and 

 Greenland. 



4. Germa iic Type the basis of the vegetation of England. 



He thinks, that while Europe has had the principal part in the coloni- 

 zation of the British islands, a great vegetable migration has also 

 taken place from America ; and that the arctic plants originating in 

 Greenland, have propagated themselves across Iceland, Feroe, and 

 Shetland, as far as the mountains of Scotland. These mountains have 

 therefore derived their flora partly from Norway and partly from 

 Greenland, by a sort of double migration. His opinion is founded on 

 the fact, that the relative proportion of plants, exclusively European, 

 which enter into the flora of Shetland, is J ; into that of Feroe, { ; 

 and into that of Iceland, -fa ; all the rest being common to Europe and 

 America. In proportion, therefore, as we remove from Europe, 

 the number of vegetables peculiar to that continent diminishes ; but 

 at the same time the proportion of the Greenland plants increases in 

 nearly the same ratio. Martins, however, does not agree with Forbes 

 in his bold and novel hypothesis, but attributes the colonization to the 

 transport of seeds from America and Europe, by means of the gulf 

 stream. This stream, he thinks, has thrown Eriocaulon septangulare 

 on the shores of the Hebrides, and, running along the coast of Scot- 

 land, carries seeds to the sandy shores of Shetland, Feroe, and Iceland. 

 He considers it the principal agent in the diffusion of European plants 

 in these islands. Winds, aerial currents, and birds, he thinks, have 

 also contribtited to the dissemination of species.* 



* For further details on the subject of the Geography of British plants consult Watson's Distri- 

 bution of British Plants, and Cybele Britannica ; Forbes's paper in the Reports of the Geological 

 Survey of Great Britain ; Martins' papers in the Edinburgh Philosophical Journal for 1849. 



