CLIMAX UNITS. 



129 



are more or less common throughout. In the scrub or chaparral formation, 

 Querais, Ceanothus, Cercocarpus, and Rhus are common genera, with one or 

 more common species. Associations show a similar relationship with refer- 

 ence to the principal and secondary species. The great majority of these are 

 the same as to genera, and the number of identical species is usually consid- 

 erable. 



From the organic connection between formation and association, it seems 

 desirable to use similar terms to designate them. For the sake of distinction, 

 however, it is necessary to employ the termination in different form. Accord- 

 ingly, it is proposed to use the roots found in hylion, helion, poion, etc., but to 

 substitute the ending -mm for -wn: Thus, the short-grass formation, BoiUeloua- 

 poion, of the Great Plains would fall into the BvMKs-BovieUmar^oium and 

 the Aristida-BouteUmor-poium. This method has the advantage of definitely 

 correlating formation and association upon the basis of life-form and habitat, 

 and of reducing the number of terms needed. The names thus constituted 

 are so few and so distinctive that there seems not the slightest danger of con- 

 fusion with neuter generic names. 



Consociation. — ^The consociation is the unit of the association. It is char- 

 acterized by a single dominant. The association is actually a grouping, the 

 consociation is pure dominance. Hence it is the most readily recognized of all 

 communities, and it has figm-ed both as formation and association. In the 

 usual treatment most consociations appear as associations. This funda- 

 mental relation between formation, association and consociation was recog- 

 nized by Pound and Clements (898 : 223, 1900 : 324) in the division of the river- 

 bluff formation into the red oak-hickory type, and the bur oak-elm-walnut 

 type, each characterized by a number of dominant species or facies. While 

 the communities are now seen to have been too restricted, the sequence of 

 formation, type, and facies is essentially that of formation, association and 

 consociation. A similar relation between the facies and consocies was recog- 

 nized by Clements (1907 : 226). As a consequence, it is but a short step to 

 clarify this relation into the exact one here established between association and 

 consociation. The association thus becomes a group of two or more consocia- 

 tions, and the word "facies" disappears in this sense at least (plate 36, a, b). 



The uniform dominance of a consociation makes its recognition a simple 

 matter. Since the consociations of an association approach each other in 

 equivalence, i. e., in response to the habitat, they are frequently mixed in 

 various degrees. Such mixtures are more or less complete expressions of 

 the association, however, and are so numerous and various that no definite 

 term is required. The Bulbilis-Bouteloua-poium consists of two divisions, the 

 Bouteloua consociation and the Bulhilis consociation; the Aristida-BoiUeloua- 

 poium of several consociations, Bouteloua rothrockii, B. eriopoda, Aristida 

 arizonica, etc. When two or more consociations are mixed, the term mictium 

 (Clements, 1905:304) may be employed when needed, as for example,a 

 Bulhilis-Bouielova-mictium would be an area of mixed grama and buffalo-grass 

 which, with the Bouteloua and Bulbilis consociations, would make up the asso- 

 ciation. Such a mictimn is, however, only the association in miniature. 



A consociation is denoted by the term -etum, a suflSx long ago proposed by 

 Schouw (1823:165) for a community characterized by a single dominant. 

 This termination has come into general use, usually for a single dominant 



