SERAL UNITS. 135 



Clans are distinguished upon the same bases as societies. They are con- 

 nected for the most part with particular aspects, and the vast majority of 

 them are aspect clans. The minor groups of layers are layer clans, and the 

 clan may also be recognized in the moss, lichen, and fungus communities. The 

 term clan is a partial synonym for community in the original sense (Clements, 

 1905 : 297 ; 1907 : 227, 240) . It comprises the conununities found in subclimax 

 and climax stages, while the invading or developing communities of initial 

 groups are termed colonies. Communities have been designated by means of 

 the suffix -are (l. c, 1905 : 299), and it is now proposed to restrict the use of 

 this suffix to the clan, e. g., Gentianare, Mertensiare, etc. 



SERAL UNITS. 



Nature and significance. — ^The units which have just been considered are 

 essentially climax communities. In addition, there are similar or analogous 

 communities throughout the course of succession. To many it will appear 

 an unnecessary if not an unwelcome refinement to recognize a developmental 

 series of units. To such students the series already established, viz, formation, 

 association, consociation, society, and clan, will suffice for all units without 

 regard to a distinction between developmental and climax phases of vegetation. 

 However, for those ecologists who regard the formation as an actual organism, 

 it is as essential to distinguish developmental and climax communities as to 

 recognize gametophytic and sporophytic generations in the life-history of the 

 individual. 



The need of such a distinction has already been at least suggested by Hult 

 (1885) and Klinge (1892) in their recognition of climax formations, and espe- 

 cially by Drude (1890 : 29; 1896 : 286) when he states that he "regards as a 

 vegetation formation each independent closed chief association of one or several 

 life-forms, whose permanent composition is effected by the definite conditions 

 of the habitat, which keep itdistinct from the adjacent formations." Schimper 

 (1898) seems to have had some idea of this distinction in his recognition of 

 climatic and edaphic formations, while Warming (1896 : 361 ; 1909 : 356) and 

 Clements (1902: 15; 1904: 134) also suggested it in distinguishing between 

 initial, intermediate, and ultimate formations. Moss (1910 : 32), in this con- 

 nection, says that: 



"As a definition of a closed, ultimate or chief association of a formation 

 this statement of Drude's is excellent, though, as his 'formation' is essentially 

 only a particular kind of association, it is not quite consistent with the views 

 of those authors who regard the formation as related to the association as 

 the genus is to the species. . . . From the point of view of succession 

 the formation of Drude, variously termed by him 'Formation,' 'Hauptforma^ 

 tion,' and 'Hauptbestand,' must be regarded as a chi^ association of a forma- 

 tion. The chief associations of a district, however, do not comprise the whole 

 of the vegetation of that district; they serve to give a vivid but somewhat 

 impressionistic picture of such vegetation; and the complete picture requires 

 the addition of the details provided by the progressive and retrogressive asso- 

 ciations, or, as these may be collectively termed, the suhardinate associa- 

 tions." (37) 



Moss (1910:36-38) further emphasizes the importance of distinguishing 

 between climax and developmental associations: 



