GENERAL 257 



trend of isotherms, stretch in a general meridian direc- 

 tion. Farther east, witli the weakening influence of 

 the westerly breezes, the distribution of warmth tends 

 more and more to conform to latitudes: hence a broad 

 division into cold, cool temperate, and warm temperate, 

 belts which find their expression in the coniferous, the 

 broad-leaf deciduous, and the evergreen hard-leaf forests. 

 In the northern region the shortness of the vegetative 

 period excludes the broad-leaf deciduous, and leaves the 

 ground to the spare and gaunt conifers, with their 

 enormously reduced and wholly protected green surface, 

 ever ready to work when the weather permits, and with 

 their store of reserve-matter in the soft wood. In the 

 southern or Mediterranean region, the brief duration of the 

 period of intense growth and the general unfavourable- 

 ness of the greater part of the year, due to winter colds 

 or summer droughts, limits the broad-leaf deciduous 

 vegetation to abundantly watered areas. The larger 

 portion of the land supports a stout, well-protected, non- 

 luxuriant type : the woody evergreen with a spare and 

 leathery foliage. 



In the northern region, the strip of coast open to the 

 Arctic winds is clear of tree-growth and is clothed with 

 low brush and moors: this constitutes a distinct belt 

 of tundras. The passage from the coniferous to the 

 deciduous belt is very gradual and is obscured by the 

 influence of soils; but the boundary between the cool 

 temperate and the warm temperate regions, i. e. between 

 the deciduous and the mediterranean vegetations, is de- 

 fined by mountain ranges such as the central plateau of 

 France, the Alps and their outspurs in Illyria, and by 

 the Rhodope range. 



If differences between the east and the west of Europe 

 are observed in the vegetation of the northern coniferous 



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