136 



SOIL CONDITIONS AND PLANT GROWTH 



Numerous chemical analyses of the peats have been made 

 by Tacke at Bremen (278), Gully (116), Micheletand Sebelien 

 (199) and others.^ 



As a general rule, though with many exceptions, the per- 

 centage of nitrogen varies with that of the lime, and the high 

 moor contains least of these, the low moor a larger quantity, 

 and the fens a still larger quantity (Table XXXIX.). 



Table XXXIX. — Nitrogen and Calcium Content of Various Peats. 



The investigations on the cause of the acid properties of 

 peat are dealt with on p. ill. 



Humus of Forest Soils. — An admirable series of studies has 

 been made by P. E. Miiller (206) of the types of humus oc- 

 curring in the Danish forests.^ In beech forests he found two 

 types, which he called mull and torf, our nearest equivalents 

 being mould and peat. On mull the characteristic plants were 

 Asperula odorata with its associated Mercurialis perennis, Mi- 

 lium effusum, Melica uniflora, Stellaria nemorum, and others, 

 moss being absent. The mull itself was only a few inches 

 thick, and was underlain by i to 5 feet of loose soil, lighter in 

 colour than mull, but almost equally rich in organic matter ; 

 still lower came a compact but porous layer of soil. The 

 surface of the soil was covered by a layer of leaves, twigs, etc. 

 Earthworms were numerous throughout ; their potent influence 

 in the soil had recently been shown by Darwin {76). Detailed 

 chemical examination was not made : it was shown, however, 

 that mull was free from acid and contained about 5 to i o per 



^ See yahresber. Agrik. Chem., 1878, p. 29 ; 1904, pp. 87, 88, etc. 

 ^ Other investigations on forest humus are dealt with by Ramann, Forstliche 

 Bodenkunde u. Standortslehre, 1893. 



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