THE CLASSIFICATION OF COMMUNITIES 371 



2. Attached. 



a. Dependent communities growing on bark, incapable of further 

 development, e.g., Schizogonion cruenti, Graphidion scriptae, Xan- 

 thorion, Usneion, etc. (Ochsner). 



b. Communities growing on soil, with capacity for further development. 



(1) With few species, ecologically simple, on soil and rock. 



(a) Communities of soil algae and crustose Uchens of short 

 duration, often pioneer stages, e.g., Zygogonium, Cysto- 

 coccus, and Stereonema communities. 



(b) Endolithic and epilithic communities of rocks, e.g., Gloeocap- 

 seta, Aphanocapseta (Fritsch, 1922), crustose lichen 

 communities. 



(c) Submersed attached algal communities, e.g., Acetabularie- 

 tum, Schizotricetum (Schroter, 1902; Baumann, 1911, p. 

 494). 



(2) Moss and Uchen heaths, with more numeK)us species and better 

 ecologic organization. 



II. Two- or more-layered, 1 mostly rooted communities. 



1. Open communities of slightly related commensals, mvolving competition 

 for place to germinate and for food. 



a. Chmatic climax communities without capacity for further develop- 

 ment, communities of deserts and desert steppes. 



b. Edaphic; mostly pioneer communities: communities of sand dunes, 

 talus, rock crevices, e.g., Ammophilion, Potentilletalia. 



2. Closed communities. Competition for place to germinate, for space, 

 and for food. 



a. Stabihty low. Constituents predominantly therophytes. Often 

 ephemeral communities of cultivated land, ditches, etc., due to man; 

 e.g., Nanocypereto-Polygonetalia, ChenopodietaUa. 



b. More stable communities with closer union. 



(1) Biologically uniform, often crowded communities of water and 

 swamps with few species. 



(a) Submersed aquatic communities, e.g., LitorelletaUa and 

 Potametalia. 



(b) Emersed communities of still waters, rooted in mud, mostly 

 with few species; often forming extensive uniform crowds; 

 swamp communities, e.g., Phragmitetalia, SaUcornietalia. 



(2) Bioecologically multiform communities of solid ground, mostly 

 with numerous species. 



(i) Few-layered communities without dominant trees or shrubs; 



(a') Aerial layering indistmct. Little influence of layers 

 on one another. Flat moors, meadow, and tall-herb 

 communities (grass-herb vegetation), e.g., Molmietalia, 

 Brometalia, Caricetaha curvulae, Seslerietalia, etc. ^ 



(b') Persistent double layering. More or less distinct 

 influence of each layer on the other; 



(c') Ground layer more or less open, dominated by the layer 

 above, which is rarely absent; Dwarf-shrub com- 

 munities, e.g., Rhodoretaliaj 



1 Including root layers: 



