DECOMPOSITION OF ORGANIC MATTER IN THE SOIL. 249 



pasteurianus (or both), may come to the fore. The cleavage products 

 then include alcohols, organic acids and carbon dioxide. With B. 

 (Clostridium) pasteurianus butyric acid is one of the prominent cleavage 

 products. When combined nitrogen is also added to the culture 

 solution other organisms will develop prominently, notably members 

 of the subtilis group, butyric bacteria, aerogenes, etc. In the soil 

 itself the addition of sugar leads to a very marked increase in num- 

 ber and, if acid production is favored, molds may subsequently become 

 prominent. In general it may be said that butyric, propionic, acetic, 

 formic and lactic acid, and ethyl, propyl, butyl and iso-butyl alcohol are 

 common cleavage products. 



In the case of starch, pectins and pentosans, similar conditions hold 

 good. Diastatic enzymes seem to be produced by various bacteria, as 

 well, as molds and streptothrices. Members of the subtilis group and B. 

 fluorescens seem to be able to transform starch into sugar without difficulty. 

 It needs hardly be added here that the vast quantities of organic acids 

 and of carbon dioxide thus formed must play an important role in the 

 breaking down of the mineral constituents in the soil. 



FATS AND WAXES. 



ORIGIN AND DECOMPOSITION. Plant substances contain varying 

 proportions of fats and waxy materials. In the dry matter of grasses and 

 cereal straw crude fat is usually present to the extent of 1.5 to 2.0 per cent. 

 In hay made from clover and other legumes the proportion of crude fat 

 is rather more than 2 per cent. In cereal grains it may range up to 

 4 or 5 per cent while in soy beans the content of crude fat is 19 per cent, 

 in germ oil meal 22 per cent and flax seed meal 34 per cent. 



Under the influence of enzymes produced by molds, yeasts and bac- 

 teria the fatty acids occurring as glycerides are decomposed into glycerin 

 and fatty acids. The extent of fat decomposition, brought about largely 

 by molds in the opinion of some, is shown by numerous experiments 

 with peanut cake, olive press cake, cottonseed meal, almond oil, corn 

 meal, etc. In a number of these experiments Aspergillus niger seemed 

 to be particularly efficient in decomposing fats. Analogous decompo- 

 sition processes may occur in the soil as proved by the experiments of 

 Rubner. 



