THE NEW FIELD-BOTANY 359 



whicli we proceed to explain have been adopted by the 

 Central Committee for the Survey and Study of British 

 Vegetation. 



First there is the Formation. Warming defines this 

 as " a community of species, aU belonging to definite 

 growth forms, which have become associated together 

 by definite external (soil or climatic) characters of the 

 habitat to which they are adapted." Elsewhere it has 

 been defined as " the vegetation of a district determined 

 by climate and soil." The plants which are associated 

 with moorlands constitute, in their whole complex, a 

 moorland formation. The vegetation of a sand-dune 

 is a dune-formation. The formation embraces one or 

 more Associations, which are smaller plant-communities, 

 related to the formation as species to a genus. Then 

 within an association there may be Societies, still smaller 

 communities, composed of aggregations of individual 

 species. Take, by way of illustration, the plant-for- 

 mation associated with clay soils. This formation may 

 embrace a woodland and a grassland association. The 

 woodland association, in its turn, may have, here and 

 there, aggregations of individual species — that is, 

 societies of Wood Anemones, Wood Sorrel, Wild Hya- 

 cinths, Primroses, and Dog's Mercury. The formation 

 is closely related to a definite habitat, and in thinking of 

 it the ecologist has in mind not only the plants that 

 enter into the formation, but the habitat in which they 

 live. A formation hag been likened to a city in which 

 there is a nice balance of human coteries, and in the 

 minds of some it is regarded as being analogous to the 

 formation of the geologist, which is composed of various 

 strata and zones. 



