210 ZONES AND REGIONS 



subject to a more or less rapid change, attributable, as regards the flora, 

 partly to historical causes and partly to the inequality in the climatic 

 humidity, but as regards vegetation, to the climatic humidity exclusively. 

 According to the nature of the atmospheric precipitations, either the 

 woodland, grassland, or desert type predominates, and, excluding the 

 local effects of soil, the type of vegetation changes its character only 

 on passing to a climate with a different degree of humidity. Tracts of 

 land bounded by such climates may be termed districts 1 . The various 

 districts of vegetation, in contrast to the floristic zones, exhibit very 

 irregular distribution and very unequal areas. 



High mountains differ, as regards temperature and humidity, climatically 

 from the lowlands. Their regions defined by temperature are at the same 

 time those defined by atmospheric precipitations. 



Owing to the great differences between the conditions of vegetation 

 in mountains and lowlands, and to the manifold oecological relations of 

 the mountain vegetation everywhere, it appears advisable to separate the 

 treatment of high regions from that of zones and districts and to devote 

 a distinct section of the book to the vegetation on mountains. The 

 sections on zones therefore, except in cases where the exclusion of low 

 mountains or of the lower regions of mountains would be unnatural, are 

 devoted to the lowlands. 



See p. 1 60 and ff. 



