694 PRINCIPLES OF SOIL MICROBIOLOGY 



substance, in the formation of "humus." 72 The black pigment of Azof, 

 chroococcum is insoluble in chemical reagents but can be extracted by 

 boiling with strong NaOH solutions, thus also contributing to the soil 

 "humus." The same is true of a large number of fungi. 73 



To demonstrate the probable role of different groups of microorgan- 

 isms in the formation of soil "humus," it is sufficient to cite the ideas of 

 Falck 74 on the origin of "humus" in forest soils. Several processes of 

 transformation of organic matter leading to various types of "humus" 

 formation are differentiated: 



1. Mycocriny. This is the complete decomposition of organic matter by 

 fungi, whereby the raw materials (broad leaves, pine needles, roots, branches) 

 added every year to the soil are readily decomposed and there is no increased 

 accumulation of "humus." The filamentous fungi and the higher or mushroom 

 fungi (represented in the soil to a large extent also by the mycorrhiza fungi) can 

 decompose the organic matter to the end, without forming any intermediate dark, 

 humus-like substances. The carbon is either assimilated or given off as CO2, 

 the nitrogen and minerals are largely transformed into fungus protoplasm; the 

 latter forms an excellent forest fertilizer, since it is readily decomposed further. 

 The woody and crude fibrous substances may be thereby destroyed or corroded. 

 In destruction, the cellulose is decomposed completely to C0 2 through the organic 

 acid stage, more or less resistant to decomposition. The residual substances are 

 soluble in ammonia. In corrosion, the lignin crust is first attacked (by Merulius 

 and other Basidiomycetes), then the cellulose (or both at the same time) is de- 

 composed almost completely. 



2. Anthracriny. This is the process of decomposition of organic matter inter- 



72 Muller, P. E. Die natiirlichen Humusformen. Berlin. 1887. Kos- 

 tytschew, M. Ann. Agron., 17: 17-38. 1891; Koning, C. J. Beitriige zur Kennt- 

 nis des Lebens der Humuspilze und der chemischen Vorgiinge beiderHumusbild- 

 ung. Archiv. Neerland. Sci. Exact. Nat. (2), 9: 34-107. 1904; Beijerinck, 

 M. W. Uber Chinonbildung durch Strcptothrix chromogenus und Lebensweise 

 dieses Mikroben. Centrbl. Bakt. II, 6: 2-12. 1900; Wehmer, C. Zum Abbau 

 der Holzsubstanz durch Pilze. Ber. deut. chem. Gesell., 48: 130-134. 1915; 

 Waksman, 1926. 



73 Rippel, A., and Ludwig, O. Die Schwarzfarbung von Azolobacter chroococ- 

 cum Beij. als Melaninbildung. Centrbl. Bakt. II, 64: 161-166. 1925; Further 

 information on the formation of "humus" in the soil is given by Lohnis, 1910 

 (p. xiii); Heinze, B. Humusbildung und Humuszersetzung im Ackerboden. 

 Centrbl. Bakt. II, 26: 682-3. 1910; Bottomley, W. B. Formation of humic 

 bodies from organic substances. Biochem. Jour., 9: 260-268. 1915; Muller 

 and Hansendorf. Humusstudien. Ztschr. Forst. u. Jagdwessen., 53: 789-S40. 

 1921; Waksman, S. A. On the nature and origin of the soil organic matter or 

 soil "humus." I. Introductory and historical. Soil Sci., 22: 123-162. 1926. 



74 Falck, R. Mykologische Untersuchungen und Berichte. Gebr. Gotthelft. 

 Cassel., 2: 1923. 



