4 Introduction 



originally owe to Grrisebach'. It is not intended to enter 

 here into a discussion of this question, for which the 



literature must be consulted^. The uses of 

 formation *-^® terms 'plant-formation, 'plant-association 



the plant- and plant-societ'y in this book are those 



association, adopted by the Central Committee for the 

 ^^ t Toe' t Survey and Study of British Vegetation. 



Whatever may be the ultimate fate of these 

 terms it will be generally conceded that their consistent 

 use in the description of the types of vegetation of a given 

 region will afford a useful test of their appropriateness. 



The Plant-foemation 



A plant-formation is the natural vegetation occupying 

 a habitat with constant general characters which deter- 

 mine the communities of plants occurring in that habitats 



The characters, or as they are often called 

 factoS ^^^ ecological factors, of the habitat, which 



influence vegetation, are often classed as 

 climatic and edapMc. 



Climatic factors are those primarily dependent on the 

 climate of the region in which the plant-formation is 

 developed, such as temperature, precipitation (i.e. rainfall, 

 snowfall, dew, etc.), humidity of the air and wind. 



1 Grisebaeh, H. E. A., " Ueber den Einfluss des Climas auf die 

 Begranzung der natiirlichen Floren." Linnsea, xii. 1838. 



'' See especially Schimper, A. F. W. , Pflamengeographie mhf pkysiologi- 

 scher Grundlage, Berlin, 1898 (English translation, Plant Geography upon a 

 Physiological Basis, Oxford, 1903-4) ; Clements, P. E., Research Methods 

 in Ecology, Lincoln, Neb., U.S.A., 1905; Warming, E., The (Ecology of 

 Plants, Oxford, 1909; Moss, C. E., "The Fundamental Units of Vegeta- 

 tion," New Phytologist, ix. 1910 (issued separately by the New Phytologist, 

 Botany School, Cambridge) ; Ch. Flahault and C. Schrober, Phyto- 

 geographical Nomenclature, Zurich, 1910. 



^ This of course is not a logical definition but only a preliminary 

 description. The conception of a plant-formation, as understood in this 

 book, can only be made fully clear by reference to the examples dealt 

 with in Part n. 



