202 CLASSIFICATION OF PLANT COMMUNITIES 



is one which has not supported plant life before and so contains no 

 plant parts or remains, either living or dead. The substratum of a 

 primary bare area is usually sand, rock, or water. A secondary 

 bare area, on the other hand, is one on which the plant community 

 has been destroyed by one means or another. On such an area there 

 is almost certain to be some humus and there may be seeds or other 

 propagating organs that are alive. Any bare area is almost certain 

 to be either wetter or drier than the habitat of the climax association. 

 If it is wetter than the climax the succession will in general progress 

 from hydric toward mesic. Such a successional series is said to be 

 hydrarch. On the other hand, if the bare area is drier than the climax 

 the succession progresses from xeric toward mesic and the succes- 

 sional series is said to be xerarch. A successional series or sere 

 that starts on a primary sand area is called a psammosere, one that 

 has its origin on bare rock is called a lithosere, one that starts in 

 fresh water is called a hydrosere, and one that starts in salty water 

 is called a halosere. These facts lead to the following classification 

 of seres. 



Primary seres: Secondary seres: 

 Hydrarch : Hydrarch 



Hydrosere Xerarch 



Halosere 



Xerarch : 



Psammosere 

 Lithosere 



REFERENCES 



Clements, Frederic E.: Plant Succession: An Analysis of the Development 

 of Vegetation, Chapter VII. Structure and Units of Vegetation, Carnegie 

 Inst. Washington, Pub. 242, 1916. 



Gleason, Henry Allen: The Structure and Development of the Plant 

 Association, Bull. Torrey Bot. Club, 43, 463-481, 1917. 



Nichols, George E.: The Interpretation of Certain Terms and Concepts in 

 the Ecological Classification of Plant Communities, Plant World, 20, SOS- 

 SIT, S41-35S, 1917. 



A Working Basis for the Ecological Classification of Plant Communi- 

 ties, Ecology, 4, 11-23, 154-179, 1923. 



Tansley, Arthur George: Practical Ecology: A Guide for Beginners in the 

 Study of Plant Communities, New York, Dood, Mead & Co., 1923. 



Tansley, A. H. : The Classification of Vegetation and the Concept of Develop- 

 ment, Jour. Ecology, 8, 118-149, 1920. 



Yapp, R. H.: The Concept of Habitat, Jour. Ecology, 10, 1-17, 1922. 



