Chapter XI — 203 — Concept of Floral Elements 



Braun-Blanquet (1919, 1923), Reichert (1921), EiG (1931), Wan- 

 GERiN (1932), Steffen (1935), Degelius (i93s), and others. Having 

 made a study of these various viewpoints, we consider that the division 

 of a flora into elements should be based not on any one but on all of 

 the following five principles: 



1. Geographical elements, species grouped on the geographical prin- 

 ciple, according to the types of their areas, according to their 

 geographical distribution within the region whose flora is under inves- 

 tigation, and also, where necessary, according to their altitudinal distri- 

 bution. 



It would be erroneous to believe that simply by grouping the species 

 of a given flora on the geographical principle, i.e., by establishing the 

 geographical elements of a flora, one may determine the origin of that 

 flora. This may be true in part only as regards migration floras, but as 

 regards the relic and endemic species even of such floras and also as 

 regards relic floras, elements established on the basis of geographical 

 distribution do not reflect the genesis of a flora. If, for example, we 

 take arctic-alpine elements, we find that part of their area lies in the 

 Arctic and part in the Alps. But which of the component species are of 

 Arctic origin and spread from the Arctic to the Alps and which are of 

 Alpine origin and spread to the north into the Arctic regions we shall 

 not be able to ascertain by grouping the species on a geographical 

 basis. 



2. Genetic elements, species grouped according to their region of 

 origin, thus reflecting the genesis of the given flora. To determine the 

 region of origin of a species is often a very difficult matter, requiring 

 a monographic study of the genus to which it belongs. Nevertheless, 

 these difficulties are not insuperable, and the classification, if not of the 

 entire flora, at least of its chief species into genetic elements is fully 

 possible. 



3. Migration elements, species grouped according to the routes by 

 which they migrated to the given floral region, e.g., along the valleys of 

 certain rivers, along the seacoast, over definite mountain passes, or over 

 detour routes to avoid mountain chains, etc. To establish such ele- 

 ments is ordinarily very difficult and of little promise, since a species 

 may penetrate into the domain of a given flora not by a single route 

 but by several routes. Nevertheless, the establishment of even a small 

 number of such migration elements may provide valuable clues to the 

 history of the given flora. 



4. Historical elements, species grouped according to the time when 

 they became a part of the given flora {e.g., species that arose in central 

 Europe during the Wiirm glaciation or species that became distributed 

 during the arid, xerothermic period in post-glacial times). 



5. Ecological elements, species grouped according to habitat pref- 

 erences. The establishment of such elements if of great significance in 

 determining the history of a flora and of those climatic changes to 

 which it has been subjected. 



The fact that the term "element" is used in so many different 

 senses has impelled some investigators to maintain that it should be 

 used in only one of these senses and that for the others different terms 

 should be applied. Some maintain that the term "element" should be 



