58 DISTRIBUTION OF PLANTS 



It will be observed that the only apparent change 

 (other than of names) is in uniting the alpine and snowy 

 zones into the Alps. But, according to the divisions in 

 the Outlines, many species descending to the base of 

 mountains were thrown into the same zone or region with 

 others peculiar to the southern parts of Britain, and 

 never found near the mountains ; to avoid which incon- 

 gruous union, a somewhat earlier termination is given to 

 the Plains in the present work. The cessation of Em- 

 petrum nigrum was made the boundary line between the 

 alpine and snowy zones ; an insufficient distinction, since 

 the distribution of this shrub in the alpine or mossy 

 region is too irregular to become a test, and would ap- 

 pear to be more dependent on the nature of the ground 

 or surface, than on elevation. Moorland being a term in 

 common use to express heath-covered tracts at any ele- 

 vation, I have found it mislead persons, whose ideas run 

 more upon names than realities. 



1. The Region of the Plains is too well known to 

 British botanists to call for any particular description. 

 It will include all the low or open country from the south 

 coast of England to the borders of the Highlands in lati- 

 tude 56 — 56\, terminating at the sea level on the shores 

 of the Clyde and Tay. All hills attaining a sufficient 

 elevation to produce species, which are not found in the 

 low and open situations within this portion of Britain, 

 will be referred to the higher regions. The absolute 

 height at which such species grow is of little import in 

 determining the line dividing the plains and uplands, 

 since many species never found in the open country, do 

 descend almost to the sea level about the bases of moun- 

 tains or in the intervening valleys. A species ascending 

 into such situations is still called a species of the plains, 

 while one descending to the same place may be referred 

 to the uplands only. If decidedly crossing each other. 



