136 IV. PIIYSICAL GEOGRAPHY. 



Highland mountains being made evident in the addition 

 of many boreal and arctic species to the British flora, 

 which can flourish on the coasts and plains only in lati- 

 tudes still more northern than those of Scotland ; and 

 which in this country are found only on and about the 

 Highland mountains. The areas of these three latitudi- 

 nal divisions may be given in square miles thus : — 



S.Britain 38,474. M. Britain 26,555. N.Britain 22,374. 



A flora for each of these three divisions will be given in 

 the ' Summary of Distribution,' chapter V. 



6. Longitudinal divisions. — These cannot be traced out 

 so readily and satisfactorily as latitudinal divisions. 

 Three are more desirable than two divisions for geogra- 

 phico-botanical objects. Only simple or single compari- 

 sons can be made between the floral statistics of two 

 spaces ; while three spaces may frequently serve to show 

 a gradation of difference, be it in the total flora, or in the 

 several orders or other groups of systematic botany. But 

 three longitudinal divisions are found to be impracti- 

 cable ; leading to inequalities of area and altitude, which 

 would vitiate botanico-statistical comparisons between 

 the two sides of the island. Even two divisions cannot 

 be traced in any close accordance with lines of longitude 

 on maps, by reason of the oblique position of Britain and 

 its islets, its inequality of width, and the narrowness of 

 the main island, in parts where eastern and western 

 coasts approximate with only short interspaces. The 

 line of Tivo West from Greenwich cuts England into 

 western and eastern halves. By giving to that line a 

 waving obliquity from south-east to north-west, so as to 

 correspond with the western boundary line of the pro- 

 vinces, longitudinal divisions of England are obtained, 

 bearing sufficient approximation to geographical truth for 



