1 8 Origin of the British Flora. 



siderable number of plants which are confined to the 

 Eastern Counties, they, or at any rate the majority of 

 them, have not a correspondingly eastern distribution on 

 the Continent, and so many of them occur throughout the 

 greater part of Europe, that the present local distribution 

 in Britain may be, after all, climatic rather than geo- 

 graphical. The Eastern Counties are considerably drier 

 and more sunny than the others, in this agreeing more 

 nearly with the mainland of the Continent. 



Our western plants, on the other hand, are very 

 peculiar, for we find in Cornwall and Devon, and also in 

 the West of Ireland, groups of plants characteristic of the 

 Pyrenean region. These plants occur usually not as 

 rarities but in profusion, so that in parts of the West 

 of Ireland the common species which carpet the hill-sides 

 are Iberian forms unknown elsewhere in Britain. There 

 is also another peculiarity which must be taken into 

 account when we discuss the origin of these outliers — 

 though Pyrenean plants occur both in the south-west of 

 England and in the West of Ireland, the species found in 

 the two districts are not the same. Thus Cornwall pos- 

 sesses two of the Pyrenean heath-plants. Erica ciliaris 

 (another outlier of which occurs in Dorset) and Erica 

 vagans; while the four found in the West of Ireland, 

 Erica Mackayi, Erica mediterranean Dabeocia polifoliay 

 and Arbutus Unedo, are all different from the Cornish 

 ones. The only western plants common to the two 

 regions are three spurges, two of which are sea-coast 

 species. Nearly all the Pyrenean plants found in the 

 British Islands, including the only tree belonging to this 

 group, have minute seeds, the numerous large-seeded trees 

 and plants which are associated with them in Spain not 

 extending into Britain. 



Three American plants also occur in Ireland, but the 



