Flahault : Phytogeographic Nomenclature 393 



some ideas, in order to elicit thoughtful discussion, here and else- 



where. 



Phytogeographic nomenclature may be applied to two differ- 



ent things : 



1. To geographic and topographic substrata of vegetation, 

 i ■ e. , to geographic and topographic units. 



2. To vegetation itself, grouped in different ways, according to 



conditions of climate and environment, i. c, to biologic units. 

 Let us then direct our attention to the first. 



I. Nomenclature of Geographic and Topographic Units 



It will be expedient to take as the basis of fundamental di- 

 visions, essential facts which dominate all others and which are in- 

 contestable in themselves and in their reactions on vegetable life. 



The general relations of vegetation to the fundamental condi- 

 tions of climate need no discussion here. Prof. Drude * was right 

 when he endeavored to represent the fundamental climatic data in 

 such a way as to correlate essential biologic facts with their deter- 

 mining causes. Our lithosphere may thus be subdivided by lines 

 more or less parallel to the equator, into zones distinctly character- 

 ized at the same time by climate and by the vegetation which is its 

 expression. In cold countries there is a corresponding form of 

 vegetation, plants of small size with highly developed underground 

 organs, etc. ; plants which inhabit them resist very low tempera- 

 tures during their period of rest, and even during their vegetative 

 period endure temperatures below o° C; these are microthermal 

 plants. In warm countries there are corresponding plants which 

 require very high temperatures, perishing at o° C. or even at tem- 

 peratures above freezing point ; many of them have their activity 

 scarcely interrupted. These are macrothermal vegetations. In 

 temperate countries there are plants which undergo a periodical 

 rest, and which alternately endure low and high temperatures; 

 these are mesothermal. 



It is natural then to divide the terrestrial globe into cold, tem- 

 perate and warm zones, as did William Schimper f following Grise- 

 bach. Without becoming unintelligible, distinction may be made 



* Drude, Manuel, p. 69, pi. iv. 



t Schimper, Pflanzengeographie, 227. 



