I4 george E. nichols Vol- IV, No. I 



the canopy overhead and the subdominant 5 species among the shrubs and her- 

 baceous plants which go to make up the undergrowth have an important bear- 

 ing on the nature of the vegetation as a whole. It is the dominant species, of 

 course, which characterize the community in its larger aspects ; and it is with 

 reference to these that associations are commonly named. In this connection, 

 a distinction is frequently made between associations in which the position of 

 dominance is shared by two or more species (e.g., oak-hickory association) 

 and those in which a single species is dominant (e.g., pitch pine association), 

 associations of the latter type being designated consociations. 



Plant Communities of Subordinate Rank within the Association. Within 

 a plant association are commonly included various communities of lower rank, 

 which are designated societies. Societies are of two general sorts: layer 

 societies and group societies. A layer society is a plant community within an 

 association which results from the tendency of various species of smaller size 

 than the dominant life-form to display their foliage at more or less definite 

 levels. Such societies are particularly characteristic of forest associations 

 (e.g., small tree, tall shrub, low shrub, or herbaceous layer societies in an oak- 

 hickory forest). A layer society tends to be distributed more or less uni- 

 formly over the entire area occupied by an association. A group society is a 

 plant community within an association which results from the local aggre- 

 gation to form more or less well-defined clumps or masses of any species other 

 than those which predominate in the association as a whole (e.g.. a local clump 

 of sassafras trees or of rhododendron, or a mass of bryophytes on a tree 

 trunk in an oak-hickory forest). 



Seasonal Aspects of the Association. An association commonly presents 

 different aspects at different seasons of the year — i.e., periodic changes in the 

 appearance of the constituent species, associated with periods of foliation and 

 defoliation or with periods of flowering, etc., which are reflected in the 

 physiognomy of the association as a whole or of its constituent parts. 



The Association an Organic Entity. Characterized as above, a plant asso- 

 ciation may be regarded in its entirety as an organic entity, and as such it 

 occupies a position in the field of ecological plant sociology which is homolo- 

 gous in a general way to that occupied by an individual plant or specimen in 

 such fields of botany as plant morphology or plant taxonomy. As integral 

 parts of the larger community, plant societies bear a relation to the association 

 which is somewhat analogous to that borne by the various organs of an indi- 

 vidual plant to the plant as a whole. 



B. Interpretation and Application of the Term Plant Association 



Divers Interpretations. Notwithstanding the fact that the term plant 



association is now generally accepted as the designation for what is known 



as the " fundamental unit of vegetation," there has been considerable diversity 



5 Subdominance can be interpreted to mean " dominance within dominance." 



