INTRODUCTORY EXPLANATIONS. 19 



The attention of readers must now be requested to the 

 distribution of plants in Ascending or Climatic Zones, under 

 the combined influence of geogi-aphical position and con- 

 figiu-ation of sm-face. It is a familiar fact, that the climate 

 of Britain is foiuid to deteriorate and become colder, as we 

 pass from south to north ; and it is almost equally well 

 known, that a similar change is perceived, as we pass from 

 the coast hne or open plains into the mountain valleys. 

 The difference of climate between the bases and smnmits 

 of the loftier liills, is still wider than that between the 

 southern and northern extremities of the island. None of 

 the Highland hills are sufficiently lofty for their smnmits to 

 reach the line of perpetual and continuous snow, such as is 

 seen on the Alps or PvTcnees ; yet so cold is the climate 

 near their summits, that large isolated masses of snow re- 

 main immelted upon them dming the whole siunmer, in 

 ra\'ines or other hollow places, and on declivities which in- 

 cline from the mid-day sun. In the months of July and 

 August, we still find patches of snow even do^\Ti to 3,000 

 feet, among the central Grampians ; although none may 

 remain so late upon the more detached groups, whose sum- 

 mits rise much above that height. 



These differences of chmate are attended with coire- 

 sponding differences in the botanical productions of the 

 island. The botany of the south coast differs much from 

 that of the north coast : many plants of the plains are un- . 

 able to endure the colder and more humid climate of the 

 mountain valleys ; and on the summits of the Grampian 

 movmtains, we cannot find a tenth of the species which 

 may be seen between their bases and the nearest sea- 

 coasts. 



Though such facts must long have been familiar to the 

 eyes and imderstandings of botanists, they still remained 

 only unconnected facts, imtil the present wi-iter commenced 



