42 M. Martins on the Vegetable Colonisation of the 



relics of a colony whose point of departure was the north of 

 Spain. Confined to the western coast, these plants do not 

 exist in the eastern provinces of the island. We shall after- 

 wards endeavour, with Mr Forbes, to discover the probable 

 causes of this migration, the most ancient of all, since it sup- 

 poses a temperature and a distribution of lands and seas very 

 different from what they now are. 



2. Armorican Type. — The south-west of England and south- 

 east of Ireland, present us with a vegetation whose analogy 

 with that of Brittany and Normandy has long struck bota- 

 nists. Many southern species are met with along the western 

 coasts of France, until the always increasing rigour of the 

 climate arrests them in their migration towards the north. 

 A certain number of these plants still find in the peninsula 

 whose extremity is occupied by Cherbourg, a temperature so 

 mild in winter that they maintain their position there not- 

 withstanding the lateness of the summers. These plants are 

 then spread over the south-west of England, along the coasts 

 of Devonshire and Cornwall, whence they have reached the 

 opposite shores of Ireland, and have become naturalised in 

 the counties of Cork and Waterford. It was in this manner 

 that the Normans formerly left these same shores under the 

 guidance of William the Conqueror, in order to invade Eng- 

 land. But the vegetable occupation has not passed beyond 

 the south of the island; and the severity of the climate, which 

 presented no obstacle to man, formed an insuperable barrier 

 to the invasion of vegetables. 



2. Boreal Type, — The mountains of Scotland, Cumberland, 

 and Wales, present a special vegetation to the botanist, dif- 

 ferent in every respect from that of the plains of England. 

 Analogous to that of the Alps of Switzerland, this flora has 

 a still more striking resemblance to that of the arctic coun- 

 tries, such as Lapland, Iceland, and Greenland. The greater 

 number of plants which live on the summits of the high 

 mountains of Scotland, grow at the level of the sea in the 

 islands of the Icy Sea; but there are many of them which have 

 not been observed among the Alps of Switzerland. At the 

 same time the immense majority of these vegetables exist at 



