354 POPULAR GEOGRAPHY OF PLANTS. 



them. Some of the more conspicuous species are thus as- 

 certained to observe the same relative position to each other, 

 though not always growing at the same absolute height. 

 For instance, in comparing three of the lists together, the 

 beautiful but common Heath, called Ling (Calluna vulgaris), 

 is found at a greater elevation than the Juniper, and the 

 Juniper higher up than the Cross-leaved Heath (Erica 

 Tetralix). In the same way Erica Tetralix grows above 

 the Broom (Genista Anglicd), and Genista Anglica above 

 the Sweet Gale (Myrica Gale], or the common Brake 

 (Pteris aguilina). 



These conspicuous plants, growing at different heights on 

 the mountains, are then made use of as landmarks, which 

 indicate the commencement of the different zones, each 

 of which is characterized by the presence or absence of cer- 

 tain species. 



As a specimen of the method pursued, we may be allowed 

 to borrow one list of plants which was made on the highest, 

 or nearly the highest, of the Grampian Mountains, Ben- 

 muich-dhu, the summit of which is said to be more than 

 4000 feet above the sea. The flowering plants which grew 

 immediately round the cairn, which marks the highest point, 

 are first mentioned in a separate group by themselves, being 



