THE COMPOSITION OF THE SOIL 137 



cent, of organic matter completely disintegrated and most 

 intimately mingled with the mineral matter. 



Torf differed completely. The characteristic plant was 

 Trientalis europcBa with the associated Aira flexuosa and moss, 

 but surface vegetation was not very common. The loose layer 

 of leaves was absent, and the torf itself was so tough and 

 compact that rain water could not readily penetrate. Below 

 it was a layer of loose, greyish sand {bleisand), and lower still 

 a layer of reddish soil (roterde), or else a pan {ortstein). Prac- 

 tically 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. 



Torf 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 deter- 

 mined 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 earthworms mull was therefore 

 found, if not, torfv/2iS 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. 



Humus of Field Soils. — It is commonly assumed that the 

 humus of field soils is of the same nature as that of peat, fen, 

 or forest. There are undoubtedly certain properties in common, 

 Alway and Neller (3^) find that the differences in moisture 

 content of adjacent plots of varying organic matter content can 

 be explained on the assumption that soil organic matter has 

 the same water-holding capacity as the most absorbent peats, 

 i.e. three to four times its own weight. The difference in 

 organic matter was 1-37 per cent. ; the difference in moisture 



