SYNTHETIC CHARACTERS OF THE COMMUMTV 59 



flourishes or even occurs in every community of a, region, no matter how 

 broadly the communities are defined. A natural selection has taken 

 place, and a limitation of species to certain plant communities is easily 

 discernible, in which the place of each species is determined by its 

 specific potentiahties, its ecological individuality, its dependencies, its 

 ability to compete with other plants, and even by its past history 

 (migration). These factors give each species a wider or a narrower 

 field for its sociological activities. 



Degrees of Fidelity. — Five degrees of fidelity may be distinguished in 

 the attachment of the species to the given community. 



A. Characteristic Species 



Fid. 5. Exclusive species {treue): species completely or almost completely 

 confined to one community, e.g., Viola cenisia, Papaver alpinum in the Thlas- 

 peetum of the Alps, Delia segetalis in the Centunculo-Anthoceretum of Central 

 Europe. 



Fid. 4. Selective species (Jeste): species found most frequently in a certain 

 community but also, though rarely, in other communities, e.g., Phyteuma -pedemon- 

 tanurn in the Caricetum curvulae, Crepis biennis in the Arrhenatheretum of Central 

 Europe. 



Fid. 3. Preferential species (Jiolde) : species present in several communities more 

 or less abundantly but predominantly or with better vitality in one certain com- 

 munity, e.g., Luzula luzulina and Pirola unifiora in the Piceetum of the Alps and 

 the Tatra. 



B. Companions 



Fid. 2. Indifferent species (vage): species without pronounced affinities for 

 any community. 



C. Accidentals 



Fid. 1. Strange species (frenide): species that are rare and accidental intruders 

 from another plant community or relicts of a preceding community, e.g., Peuce- 

 danum palustre or Carex elata, relicts of the Caricetum elatae in the Molinietum; 

 Ammophila arenaria as a relict in the shrub communities of coastal dunes. 



Differential Species. — For sharper differentiation, especially of 

 associations or sub-associations with few or no characteristic species, 

 the so-called "differential species" are of value. These are species 

 which on the basis of the above scheme cannot be designated as 

 characteristic species of an association but normally appear only in one 

 of two or more related societies (often genetically related), Centaurea 

 jacea, Knautia arvensis, Ononis reyens are differential species of the 

 more mesic Mesobrometum as against the Xerobrometum. The 

 differential species of the three sub-associations of the Molinietum 

 coeruleae come out clearly in the association tables of W. Koch (1926). 



