THE CONSTITUTION OF THE SOIL 71 



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, 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. 



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 

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

 Eriophorum spp. and Scirpus caespitosus in elevated districts of high 

 rainfall. 



4. 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. 



5. Carr, genetically related to the fen. 



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. 



Within each of these great classes several subdivisions are re- 

 cognised, but how far they arise from differences in the organic matter, 

 or from other differences, cannot yet be ascertained. Nor is it known 

 whether any of these classes is identical with the " humus " of grass or 

 arable land. There is no doubt that a close study jointly by a botanist 

 .and a chemist woujd carry the problem much nearer to a solution. 



The observations .indicate that the mixture we have agreed to call 



