loo BACTERIA AND SOIL FERTILITY 



available to higher plants. This is very likely the explanation of 

 the beneficial results obtained when raw rock phosphate and stable 

 manure are used on phosphorus-poor soil. Microorganisms de- 

 compose the soil cellulose producing acids which react with in- 

 soluble phosphorus rendering it available to the higher plants. 

 The production of acids may at times, however, become excessive, 

 giving rise to the sour humus of moors and heaths. 



It is well-known that the fermentation processes in the soil re- 

 sulting in the decomposition of organic matter may give rise to 

 large quantities of carbon dioxid, methane, and hydrogen. The 

 hydrogen and methane do not all pass into the atmosphere, but 

 according to the researches of recent investigators furnish energy 

 to numerous other soil microorganisms, the importance of which 

 remains almost wholly for future workers to develop. The first 

 work on this subject was done by Immendorff, who in 1892 

 found that hydrogen and oxygen may be made to unite under the 

 influence of soil. He found that the oxidation of hydrogen was 

 brought about only by normal soil and not by soil previously 

 treated with chloroform vapor. This observation remained un- 

 noticed until recently when two papers appeared — one by Kaserer 

 and the other by Solmgen — which throw considerable light on 

 this phase of carbon and hydrogen transformation. They used 

 an inorganic solution containing dipotassium phosphate, ammon- 

 ium chlorid, magnesium sulfate, sodium bicarbonate, and a trace 

 of ferric chloride. This they inoculated with a small quantity of 

 soil and confined in an atmosphere consisting of a mixture of 

 hydrogen, oxygen, and carbon dioxid. Growth took place, and 

 the hydrogen disappeared. The presence of a small quantity of 

 carbon dioxid appeared to be necessary for the development of 

 the microorganisms, and it would appear that like the nitrifying 

 bacteria they can produce bacterial protein in inorganic solutions, 

 deriving their carbon from carbon dioxid. This reaction, ac- 

 cording to Lipman, is of great significance in agriculture, for a 

 great loss of energy is prevented by the bacterial oxidation of hy- 

 drogen produced in the deper layers of the soil by anaerobic f er- 

 ments. It also partly counteracts the rapid mineralization of or- 



