58 ON THE BOTANICAL GEOGRAPHY OF THE 



phenomenon. The highest mountains in this tract 

 of land afford particularly plants belonging to the 

 South of France, and to the North of Italy. 

 Another class of mountains, for instance those • 

 round Mertola, bear some plants peculiar to the 

 middle of Spain. 



The Flora of Middle Portugal is composed of 

 the foregoing, and of the northern Flora of the 

 same kingdom. It contains indeed far more 

 plants of northern Europe, particularly such as 

 are very universal, and marks as it were the 

 boundaries between both ; in the more elevated 

 parts the northern Flora immediately presents itself. 



The Flora of the North of Portugal has many 

 peculiarities. That it should be nearly the same . 

 with that of Gallicia might be expected from their 

 mutual proximity. With that of Biscay, as well as 

 with that of the Asturias, it corresponds in many 

 respects ; but not in so many as might have been 

 expected. A material cause of this difference con- 

 sists in the hills of North Portugal being of 

 granite, whilst those of North Spain are calcarious. 



