5S PLAXT SOCIOLOGY 



based on plots of 1 sq. m. it shows a larger number of casual species in 

 class I and also a greater number of species in class V. 



General conclusions can hardly be drawn from the few trustworthy 

 constancy diagrams now available. Most of the so-called "constancy 

 diagrams" of the Swedish investigators are "frequency diagrams," and 

 their data are from frequency and not constancy determinations. 



It appears from the available studies that species of the higher- 

 constancy classes can readily replace one another in different stands of 

 the same association. The writer (Braun-Blanquet) cannot share the 

 opinion that a composite framework of definite "constants," always 

 present and unexchangeable, must be considered as an essential 

 prerequisite of the association. He believes that in so far as it does 

 not concern the species which condition the society, such "constants" 

 may be replaced by non-constants, without lessening the unity of the 

 association. 



Constancy and Frequency. — Determinations of constancy can be 

 made entirely apart from determinations of frequency. If constancy 

 (in the sense of several Scandinavian authors) is combined with fre- 

 quency, it is possible, according to Kylin (1926), to obtain, at least 

 approximately, an idea of the homogeneity of the society, since fre- 

 quency touches one side of the problem of homogeneity and constancy 

 another (frequency-constancy = homogeneity in part). The "fre- 

 quency-constancy" not only gives an appreciation of the homogeneity 

 of a community but also permits the formation of a concept of the 

 sociological importance of the species of each layer of the vegetation. 

 For this the constancy figure must be added as an exponential of the 

 frequency number. If Salicornia fruticosa is found in all 20 samples 

 (1 sq. m.) from each of the 10 stands of the Salicornietum fruticosae 

 examined, the result may be written 200^°. When it is found in only 16 

 out of the 20 samples in one of the stands but in all of the samples of 

 the 9 other stands, the results may be written 196^". 



Fidelity (GeseUschaftstreue) . — The concept of fidelity has to do with 

 the sociological distribution of species. The degree of fidelity indicates 

 the more or less rigid limitation of the plant to definite plant com- 

 munities. Just as there are plants which are limited to very definite 

 soils or to a sharply circumscribed local climatic complex, so there are 

 those which are strictly confined to certain plant communities — species 

 of exclusive fidelity. But those plants are more numerous which, while 

 showing a decided preference for one or for several plant communities, 

 do not show any strong social ties. There are also species, ubiquists, 

 which flourish in quantity and are able to compete in very different 

 plant communities. Of no species, however, can it be said that it 



