DECOMPOSITION OF NON-NITROGENOUS ORGANIC MATTER 455 



that a suspension of soil or of cow feces, containing a mixed flora, 

 did not decompose any more pentosan than pure cultures of fungi. 

 Wood pentosan (alder, poplar, birch) was not destroyed in solution, 

 due to the presence of a substance inhibiting the growth of the fungi. 

 When added to the soil, 37 to 72 per cent of the wood pentosan was 

 decomposed. Pure cultures of bacteria were also found capable of de- 

 composing pentosans in the corn, varying from 1.7 to 12.8 per cent. 

 The maximum destruction of the pentosan (12.8 per cent) was made 

 by Bac. flavigena, a cellulose decomposing organism. Among the 

 other hemicelluloses decomposed by bacteria, we find also agar-agar. 86 

 Pringsheim 87 demonstrated that a trisaccharide is formed as an inter- 

 mediary product of the decomposition of mannans by bacteria. 88 



It should be noted here that, in the transformation of organic matter 

 added to the soil, the pentosans are decomposed more rapidly than 

 the celluloses and both much more rapidly than the lignins (p. 460). 



Lignins, ligno-celluloses and their decomposition. Lignin, or the non- 

 carbohydrate portion of the lignified tissues after it has been freed 

 from fats, waxes, resins and tannins, is, next to celluloses and 

 hemicelluloses, the most abundant constituent of plant tissues. 

 Sphagnum moss contains 9 to 13 per cent lignin, cereal straw 18 

 to 22 per cent, saw grass, reeds and wood 28 to 37 per cent and 

 nut shells up to 47 per cent. In the plant tissues, lignin is present 

 in a free state only to a very inconsiderable extent, but largely in the 

 form of compounds with celluloses. Ligno-celluloses are considered 

 by some to be chemical complexes in the form of esters, by others as 

 physical (incrustants) or adsorption compounds. These have a higher 

 carbon content (47 to 50 per cent) than pure celluloses, due to the 

 presence of the lignins, which contain 62 to 64 per cent carbon. The 

 exact chemical nature of the lignin itself is still a matter of dispute. 



The cell wall of plants consists of practically pure cellulose in the 

 early stages of growth, but this is changed into ligno-cellulose with 

 advancing growth, the lignin is formed from carbohydrates originally 



86 Gran, H. H. Studien iiber Meeresbakterien. II. Uber die Hydrolyse des 

 Agar-agars durch ein neues Enzym, die Gelase. Bergens Mus. Aarborg, 1902, 

 H. I. Biernacki, W. Bacterium nenckii Biern., ein neuer den Agar verflus- 

 sigender Mikroorganismus. Centrbl. Bakt. II, 29: 166-169. 1911. Gray and 

 Chalmers, 1925 (p. 199). 



87 Pringsheim, H. Uber den fermentativen Abbau der Hemicellulosen. 

 Ztschr. physiol. Chem., 80: 376-382. 1912. 



88 See also Cramer. Inaug. Diss. Halle. 1910. 



