134 STRUCTURE AND UNITS OF VEGETATION. 



ditions, much as in the consociation, it seems appropriate that it should like- 

 wise bear a locative sufl&x. For these reasons the suffix -die is retained to 

 designate societies in general and aspect societies in particular. It may well 

 serve also for thallophytic societies, e. g., Funarile, MarchanMU, Cladonile, 

 Agaridle, since the generic name clearly indicates the life-form. When it 

 seems desirable to distinguish layer societies, it may likewise be done most 

 simply and briefly by means of a suffix. Since the suffix -anum, already used 

 for layer, is unnecessarily long, it is proposed to replace it by -en, e. g., Frag- 

 arien, Thalidren, Erythronien, Helianthen. Where mixed societies exist there 

 is no better method than to combine the two generic names, e. g., PsorcUea- 

 Helianthile. 



Changes of rank or dominance. — Since consociation and society are based 

 chiefly upon dominance as controlled by habitat, it sometimes happens that 

 the dominance changes to such a degree or over such an area that the com- 

 munity loses its usual rank. A consociation may appear to be a society, or 

 even a clan. A society may assume the appearance of a consociation, or, 

 on the other hand, may likewise be so reduced as to resemble a clan. Such 

 changes in value occur most frequently (1) in or near transition areas, (2) as 

 a result of temporary oscillations of climate, and (3) in the course of succes- 

 sional development, during which consociations may dwindle to insignificant 

 groups, or colonies which appear to be societies or clans develop into consocia- 

 tions. The last is typically the case with such undershrubs as Gutierrezia, 

 Artemisia, Yucca, etc., which often appear as clans and societies in grassland. 

 These conomunities, however, are really the beginnings of a postclimax con- 

 sociation, the fuU development of which is conditioned upon a climatic change. 



It is possible to treat communities of this sort solely with reference to their 

 actual value in a particular association, without regard to their normal or 

 developmental relation. Such a method is simpler and more convenient, 

 but it has the disadvantage of obscuring the organic relations and of confusing 

 the facts of development. Consequently it is thought best to regard consocia- 

 tions and societies as entities, which may increase or decrease markedly in 

 dominance and extent under certain conditions. However, if the facts are 

 made clear, it matters httle whether a particular group is called a reduced 

 consociation or a society which represents a consociation of a contiguous area. 

 Theoretically it is possible, at any rate, that a consociation of one regiomnay 

 be changed into a typical society in another. 



Clan. — ^A clan is composed of a secondary species. It is next below the 

 society in rank, though it is not necessarily a subdivision of it. Clans may 

 and usually do occur in societies, but they are also found in consociations 

 where there are no societies. A clan differs from a society chiefly in being 

 local or restricted to a few small and scattered areas. Its dominance is small 

 or lacking, though it may often furnish a striking community in the vegeta- 

 tion. While societies and clans can usually be distinguished with readiness, 

 there is no hard and fast line between them. Even the use of quadrat 

 methods can not always distinguish them clearly. A clan differs from a colony 

 in being a more or less permanent feature of climax communities or of consocies 

 which exist for a long time. A colony is a group of two or more species which 

 develops in a bare area or in a community as an immediate consequence of 

 invasion (plate 38, a, b). 



