394 Flahault : Phytogeographic Nomenxlature 



between the cold and temperate zones according to the hemisphere 

 which they occupy. Prof. Drude has done this for the general 

 grouping of the regions of vegetation in publishing sheet 46 of 



Berghaus' Physical Atlas. 



This grouping is only of general value. It permits a first sep- 

 aration, a division of the earth comprehensible to persons who are 

 not prepared for special study. It is destined only to facilitate 

 subsequent grouping, to render it even possible. The tropics are 

 not the limits of the tropical flora ; the Arctic circle does not in- 

 dicate exactly where certain floras either commence or end ; 

 for which reasons it seems preferable to express the most impor- 

 tant climatic character of each of these zones, to distinguish them 

 simply under the names of warm, temperate and cold (in place of 

 tropical, temperate and arctic). In this case, the word zone is 

 used in the sense that is generally given it in French. 



The definition of zone exactly applies to these units of the first 

 order ; they are divisions of the sphere's surface included between 

 two parallel lines ; this is the signification of the word as adopted 

 by meteorologists, but it seems impossible to us not to apply it to 

 the belts following which the mountain flora becomes divided. 

 Another term cannot be found to replace it ; that is why this point 

 will have to be reconsidered later. 



The great warm, temperate and cold zones are respectively 

 divided into less important groups. Climatic causes combine in 

 each fundamental zone in different methods, to effectuate, on the 

 whole, very different climates, to allow the development of vege- 

 tation of varied aspect and composition. The differences in the 

 character of vegetation of two neighboring countries explains the 

 dissimilarity of their climates, and their resemblance is the expres- 

 sion of their joint climatic factors. In other words, a like en- 

 semble of climatic conditions combining in the same way deter- 

 mines a like type of vegetation ; other conditions, or only another 

 division of the same conditions, give occasion for the development 

 of types of different vegetation. So it is that the vegetative type 

 of our western Europe is that of the forest composed of trees w 

 deciduous leaves ; while that of eastern Europe is the steppe ; that 

 of the warm and constantly humid climate of the tropics, is the 

 forest which is always green. 



ith 



