16 



their developments: swamp and marsh J generally leads to two main 

 forms, muld (e. p. vegetable mould of Darwin; ordinary humus of 

 Warming) and mor< (raw-humus of German terminology). - 



The muld consists of the mineral soil in intimate mixture with 

 remains of plants and animals in various degrees of decomposition. The 

 mixing is carried on in nature mainly by animals, especially earth- 

 worms; the organic refuse is quickly decomposed (in the woods as a 

 rule in the course of a year) and the decomposition is effected in the 

 main by bacteria, which by energetic cellulose fermentation and sub- 

 division of the peptones rapidly brings the constituents of the refuse 

 masses into circulation again. The nitrogenous compounds are decom- 

 posed under development of nitric acid. The natural muld soil has 

 an aggregate structure (gritty) and is loosely deposited, thus easily 

 permeable by air and water; it reacts neutral, faintly acid or faintly, 

 alkaline. 



The phanerogamic vegetation on this soil varies according to the 

 warmth and light of the place, the moisture of the soil and its content 

 of assimilable mineral constituents. - 



The mor is formed, when the organic refuse is deposited above 

 the mineral soil, the fusion element, the animal life, being absent or 

 where the latter for various reasons is unable to carry out the mixing 

 of the soil and the humous elements w^ith sufficient energy. In the de- 

 composition, humifaction, of the organic refuse above the soil the fungi 

 play a prominent part, the bacteria a more subordinate role. Decom- 

 position proceeds slowly, extending often over many decades, and dur- 

 ing this process large quantities of humic acids are developed (colloi- 

 dal, non-absorptive saturated humous materials). On being carried 

 down into the mineral soil by rain-w r ater, these acids withdraw from 

 the soil's uppermost layer a large quantity of decomposable mineral 

 compounds (iron salts, hydrate of lime, alkalies and alkaline earths 

 etc.), which by absorption are deposited at some distance from the 

 surface and may give rise to the formation of hardpan. Even the 

 uppermost humus layer has a variable texture, from loose deposits to 

 a very dense and firm felt; the washed-out layer under the mor is 

 always dense with very small porous capacity ( pore-volume ) ; the 

 hardpan layer may vary from being earthy and loose to a perfectly 

 dense and firm, stone-hard layer, impermeable by plant roots, with 

 its single grains fused together by colloidal, humic compounds. The 

 soil always reacts strongly acid. The bacterial vegetation in the mor- 

 covered areas decreases greatly, both in number of individuals and in 

 virulence, with little ability to decompose cellulose and to split up the 

 peptones, and with reduction or cessation of the development of nitric 

 acid. In further stages of the mor -formation and especially in the 

 old deposits of this kind a considerable portion of the nitrogenous 

 compounds of the organic refuse is fast bound in resistant fungal my- 



