62 OFXOLOGICAL FACTORS AND THEIR ACTION sect, i 



forms a cold soil, because it is usually rich in water. Neither bacteria 

 that produce nitrates, nor other bacteria, nor earthworms, can thrive in 

 peat, because of its acid contents. Further details in regard to peat will 

 be given in Section VI. 



(b) Raw humus is a ' production of peat in the dry ' ^ a black or 

 black-brown peat-Hke mass, which is built up of densely interwoven, 

 incompletely decomposed plant-remains, consisting of roots, rhizomes, 

 leaves, mosses, fungal hyphae, and the like. Certain plants in particular 

 give rise to raw humus, because they bear very thin, numerous, richly- 

 branched roots (or rhizoids), which lie at the surface of the soil and 

 weave the plant-remains into a dense felt work ; such species are, for 

 example, Fagus, Calluna, Vaccinium Myrtillus, Picea excelsa. According 

 to the constituent forming the main mass, we speak of heath (Calluna) 

 raw humus, moss raw humus, beech raw humus, spruce raw humus, 

 silver-fir raw humus, oak raw humus, pine raw humus and so forth.^ In 

 plants growing on raw humus mycorhiza is frequent. Raw humus may be 

 so rich in plant-remains as to be employed as fuel (heath-peat) ; it may 

 contain from fifty to sixty per cent, of organic matter. As it forms so 

 dense and tough a felt above the mineral soil, on the one hand, it excludes 

 air (oxygen) from the subjacent layers and, on the other, sucks up water 

 as greedily as a sponge and holds it with great force ; in rainy European 

 climates it is frequently wet for a large part of the year. Consequently 

 in it, as in peat, free humous acids are produced in abundance. Like 

 peat, it has an acid reaction. There occur in it only few animals, mostly 

 Rhizopoda and Anguillulidae, but no earthworms. The part played by 

 bacteria has not yet been ascertained. Raw humus appears in forest, 

 especially in places exposed to wind, whilst ordinary humus, with its 

 earthworms and other animals, reigns in fresh places sheltered from 

 desiccation ; when ordinary humus in beech-forest has given way to 

 raw humus, because of timber-falls and such like, then the beech, being 

 no longer capable of regenerating, disappears, and is often replaced by 

 Calluna-heath.^ 



The production of raw humus is linked with lowness of temperature, 

 and is promoted by moisture.* 



The formation of a layer of raw humus also induces in the constitution 

 of the subjacent layers of soil great changes, which have become best 

 known through P. E. Miiller's ^ pioneer researches in Denmark, the main 

 results of which are given in the succeeding paragraphs.^ 



From the raw humus, humous acids and their compounds descend 

 with rain-water into the subjacent sand, which has been more thoroughly 

 washed out and is poor in soluble salts ; here they are oxidized by contact 

 with inorganic (particularly ferric) compounds rich in oxygen, and there 

 arise, for example, freely soluble ferrous compounds, which are carried 

 by water containing carbonic acid down from the upper layers of soil. 

 These layers are consequently decolorized, lose their absorbent faculty 



' P. E. Miiller, 1878, 1884, German edition (1887, p. 45). 



* P. E. Miiller, in the German edition of his worli, employs the terms heath-peat, 

 moss-peat, beech-peat, etc., in this connexion. 



' P. E. Miiller, loc. cit. * Ramann, 1895, p. 125. 



' P. E. Miiller, loc, cit. 



^ Also see Ramann, 1886, 1905 ; Warming, 1896 ; Friih and Schroter, 1904. 



