230 VEGETABLE COLONIZATION. 



country ; the former as a botanist, the latter as a zoologist and geolo- 

 gist. One important, indeed capital, fact gives the result at which 

 they have arrived, namely, that the British isles present not a single 

 plant exclusively their own, and which, with one sole excej^tion, is 

 not found likewise in continental Europe. The exception is the 

 unique species Eriocaulon septangulare, a native of North America, 

 which has been cast on the shores of the Hebrides. The British isles, 

 then, cannot be considered a centre of vegetation, since the plants which 

 inhabit them exist more abundantly on the European continent. But 

 all have not come from the same regions, and we shall be able to dis- 

 tinguish with Messrs. Watson and Forbes a series of vegetable migra- 

 tions which have colonized in succession the islands referred to. 



Asturian type. — Thanks to the mildness of its winters, Ireland has 

 preserved for us, so to say, the remains of a peninsular flora. We 

 find growing wild in the southwest of this island a dozen plants, 

 natives of the Asturias, which have maintained themselves in Ireland 

 like the last representatives of a colony whose point of departure is to 

 be found in the north of Spain. Limited to the western coast, these 

 plants do not exist in the eastern provinces of the island. Farther 

 on we shall seek with Mr. Forbes to discriminate the probable causes 

 of that migration, the most ancient of all, since it supposes a temper- 

 ature and a distribution of lands and seas very different from those 

 which exist at present. 



Armorican type. — The southwest of England and southeast of Ire- 

 land present a vegetation whose analogy, with that of Brittany and 

 Normandy, has long attracted the notice of botanists. Many southern 

 species are to be met with along the western coasts of France, up to 

 the point where the steadily increasing rigor of the climate arrests 

 their migration towards the north. A certain number of these plants 

 find, in the peninsula of which Cherbourg occupies the extremity, so 

 mild a winter temperature that they maintain their ground in spite 

 of the heat of the summers. These have afterwards spread themselves 

 in the southwest of England, along the coasts of Devonshire and 

 Cornwall^ whence they have gained the opposite shores of Ireland and 

 have become naturalized in the counties of Cork and Waterford. It 

 was thus that the Normans formerly passed from the same region, 

 imder the conduct of William the Conqueror, to invade England. 

 But the vegetable occupation has never penetrated beyond the south of 

 the island, and the rigors of the climate which could not arrest the 

 progress of the men have opposed an insuperable barrier to the inva- 

 sion of the plants. 



Boreal type. — The mountains of Scotland, Cumberland, and Wales 

 offer to the botanist a vegetation entirely special, and different in all 

 points from that of the plains of England. Analogous to the vegeta- 

 tion of the Swiss Alps, this flora presents a still more striking resem- 

 blance to that of the arctic countries, such as Lapland, Iceland, and 

 Greenland. The greater part of the plants which subsist on the sum- 

 mits of the high mountains of Scotland vegetate at the level of the 

 sea in the islands of the Frozen ocean ; but there are many of them 

 which have never been recognized in the Alps of Switzerland. By 

 far the greatest number, however, of these vegetables exist at the 



