Flahault : Phytogeographic Nomenclature 397 



Domains themselves may be divided into sectors ; secondary 

 climatic characters interpreted by vegetation will be taken into 

 account, but the consideration of botanic elements of which we 

 have not had to take account until now, also intervenes. When 

 a portion of a region or a domain may be characterized by a 

 certain number of plants which have entered from other countries, 

 it would constitute a sector. In the Atlantic domain an Aqui- 

 tanian sector may be distinguished where there are numerous 

 species which have immigrated from the Mediterranean region, 

 and where these fail, an Armorican sector ; in the French domain 

 of the Mediterranean region, there is a Provencal sector where 

 representatives from the Italian domain are abundant, Roussillon 

 and Corbieres sectors which have been invaded by Iberian species, 

 notwithstanding the barrier of the Pyrenees ; in the Iberian domain 

 an Andalousian sector characterized bv manv 



M 



etc. 



A 



graphic or topographic causes or on the physicochemic character- 

 istics of the soil influencing vegetation. 



District, such as we understand, it together with Prof. Briquet, 

 corresponds to the Bezirk of Prof. Engler. 



Islands separated from adjoining land by more or less ex- 

 tensive arms of the sea become characterized as districts by the 

 appearance of endemic types. Ridges, exceeding the limits of 

 vegetation, which separate valleys, tend to give to them special char- 

 acters by preventing migration and in favoring endernism. Moun- 

 tain ranges of a known mineralogic composition, isolated in th< 

 center of a group of different composition, may often be dis- 

 tinguished as districts for the same reason. C. Schroter, John 



Alps. 



J 



the 



Mediterranean region 



of 



of the Mi 



the Balearic Islands with their many endemic species, makes a very 

 distinct district in the western sector of the Iberian domain. 



Subdistricts may also be distinguished if they prove useful after 

 a careful analysis. It is possible that some day the opportunity 



