134 SOIL CONDITIONS AND PLANT GROWTH 



of various kinds, and in this country the work has been done 

 largely by Dr. Moss and other members of the British Vege- 

 tation Committee (279). At least three great classes and 

 another two that may be transition forms were recognised : — 



I. Dry peat (the German Trockentorf) found on heaths in 

 relatively dry regions and on poor sandy soils. It is often 

 only a fraction of an inch in thickness, and is largely formed 

 by lichens and mosses {e.g. Cladonia rangiferina, Polytrichum 

 piliferum, and others). The dominant plant is Calluna. Much 

 of the organic matter of heath soils, however, often consists 

 of undecomposed vegetation, e.g. bracken fronds, etc. 



\a. In wetter districts the layer of peat becomes thicker, 

 and no doubt changes in composition, but it still carries 

 essentially " heath " vegetation, although it shows resemblances 

 to 2. 



2. Wet peat (the German Hochmoor) formed in wet tracts 

 or regions of high rainfall, and accumulating to so great a 

 depth that it entirely determines the character of the vegetation 

 whatever the underlying rock. It receives no supplies of 

 spring or underground water, and, therefore, no dissolved 

 salts ; the drainage water is acid and poor in soluble mineral 

 matter. Two great divisions are recognised : lowland moors 

 or mosses, formed in low-lying wet places largely from sphag- 

 num, cotton grass {Eriophoruni), and Calluna; and upland 

 moors, formed mainly from Eriophorum spp. and Scirpus 

 C(Bspitosus in elevated districts of high rainfall. 



3. Fen {Niedermoor in German, see (299)) formed from a 

 calcicolous vegetation {Phragmites, Cladium, Scirpus, Carex, 

 etc.), in presence of calcium carbonate and soluble mineral 

 salts, showing no acid properties and giving alkaline drainage 

 waters. 



3«. Carr, genetically related to the fen, containing much 

 decaying tree residues, and formed in what at one time was a 

 marshy wood. 



Between fen and peat several transition forms have been 

 described by Weber (299) and also recognised in England. 

 Some of our moors are built up on older fens. 



