THE CONSTITUTION OF THE SOIL 69 



sand], and lower still a layer of reddish soil (roterde], or else a pan 

 (prtstetri). Practically no earthworms were found in the torf, but there 

 were numerous moulds and fungi, Cladosporium humifaciens Rostrup 

 and Sorocybe Resince Fr. being perhaps the commonest 



Tor/was acid, contained about 30 per cent of organic matter not 

 completely disintegrated, nor well mixed with the mineral matter. 

 It was not very favourable to the growth of young trees, and the 

 forest tended to become an open heath as the old trees died. 



The distribution of mull and torf did not seem to be determined 

 by the nature of the soil, or by the amounts of soluble alkali salts or 

 calcium carbonate present, but rather by the nature of the living 

 organisms in the soil. Animals, especially earthworms, gave rise to 

 mull, fungi produced torf. If the conditions were favourable to earth- 

 worms mull was therefore found, if not, torf was produced. The 

 nature of the vegetation was also a factor: oak only rarely formed 

 torf but commonly gave rise to mull, at least two varieties of which 

 were observed ; pine, like beech, could form either torf or mull, while 

 Calluna vulgaris and vaccinium myrtillus generally produced torf. 



Observation work on similar lines has been carried on in this 

 country by Dr. Moss and other members of the British Vegetation 

 Committee (280). At least three great classes and another two that 

 may be transition forms were recognised : 



1. Dry peat (the German Trockentorf) found on heaths in rela- 

 tively 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, Polytrichmn 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. 



2. 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 (3). 



3. 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. Sphagum, cotton grass 

 (Eriophormri), and Calluna ; and upland moors, formed mainly from 

 Eriophorum spp. and Scirpus caespitosus in elevated districts of high 

 rainfall. 



