116 Floristik, Geographie, Systematik etc. 



has been secured through the control of an editor whose work, if 

 less obvious, has nevertheless been considerable. 



The introduction discusses units of Vegetation. On the one hand 

 a vegetation-unit corresponds to a habitat with definite characte- 

 ristics, on the other hand it is a plant-community or group of species 

 associated under definite conditions. The plant-formation is deter- 

 mined by certain effective ecological "master-factors", which in 

 Britain are edaphic more often than climatic. Plant-formations 

 with obvious habitats, (e. g. salt marsh and sand dune) are easily 

 determined, but in others different growth-forms (forest, grassland, 

 heath, etc.) must he included within the same formation owing to 

 natural processes of development or succession and to retrogressive 

 changes either natural or brought about by man. As subordinate 

 units, the plant-association and the plant-society are recognised. 



Part I (p. 15—61) is a summary of the physical features , climate 

 and soils of Britain, mainly with reference to those factors which 

 more directly influence plant distribution. The account has been 

 carefully compiled and submitted to competent authorities before 

 publication, so that for the geographer in the wider sense it is of 

 special importance. 



The existing Vegetation of the British Isles is dealt with in 

 Part II. 



The opening chapter takes up such topics as the distribution of 

 the chief forms of Vegetation, the extent and location of forest, 

 moorland, and cultivated land, and changes in the forest area 

 resulting from disforesting. A summary of the existing Vegetation 

 classified mainly according to physiognomy includes the following 

 types — woodland, grassland, heathland, moorland, fenland, and 

 maritime types. A noteworthy feature in the treatment of existing 

 Vegetation is the recognition that while these physiognomic types 

 are useful in describing Vegetation, certain of these are so closely 

 interlinked that they cannot be separated in a hard and fast man- 

 ner. This is illustrated in the chapters (II— VI) on the Vegetation 

 of relatively dry soils, with no outstanding excess of water and 

 peat. Over these soils, forest is or was almost universally the final 

 stage of natural Vegetation. The plant-formation of clays and loams 

 (chap. II) was primarily oakwood characterised by Querais Retour, L. 

 (= Q. pedimculrtta, Ehr.). As retrogressive phases of this there are 

 now considerable tracts of „coppice-with-standards", also "scrub- 

 associations", and the ultimate phase of degeneration — "the neutral 

 grassland association". Owing to the oecurrence of claylands mainly 

 in plains and Valleys, much of this type of soil is now cultivated. 



The Vegetation of the coarser sands, sandstones and other sili- 

 ceous soils (chaps. III — V) is typically "dry sandy oakwood" [Quer- 

 cetutn arenosum, Roburis et sessiliflorae) or heatland. "The heath 

 formation" is discussed at considerable lenght, as regards compo- 

 sition and origin from former forest. A link between heath and 

 woodland is recognised in the oak-birch-heath characteristic of south- 

 eastern England and the course of degeneration described for this 

 suggests the processes which have led to the present wide oecur- 

 rence of Calluna heath, grassheath, and other associations. The 

 pinewood association is also placed in the heath formation. 



The Vegetation of calcareous soils (chap. VI) presents three well- 

 marked sub-formations, hitherto not fully differentiated as elements 

 of British Vegetation. On the older limestones the ashwood is cha- 

 racteristic and is linked through scrub-associations with the lime- 



