180 MINERALIZATION AND SOLVENT BACTERIA 



Iron. The iron bacteria resemble the sulphur bacteria greatly in 

 their metabolic activity. The best known of these organisms are 

 the Cirti'jthrix polyspora, Chlamydothrix ochracea, and SpirophyHum 

 ferrugineum. Winogradsky considers that the iron is deposited in the 

 sheath of the organisms due to a physiological reaction, the organ- 

 isms oxidizing ferrous to ferric compounds : 



4FeCO 3 + 6H 2 O + O 2 2Fe 2 (OH) 6 + 4CO 2 



The energy so liberated is utilized in their growth. However, the 

 investigations of Molisch, Adler, and Ellis show that they grow well 

 in a medium devoid of iron and that the precipitation of the iron is 

 due to chemical and mechanical processes independent of the physio- 

 logical activity of the organism. They play a great part in the 

 deposition of bog-iron, though not the only cause, for Molisch con- 

 siders that well-known physio-chemical agencies often play an 

 important part in the process. Manganese may at times be found 

 in the sheath of Crenothrix, in large quantities. 



Potassium. This element is required by all plants in compara- 

 tively large quantities, and the total supply in nearly all soils is 

 exceedingly large as compared to crop requirements. Yet potas- 

 sium is quite extensively used as a fertilizer, and this with beneficial 

 results. This is due to the fact that its addition to a soil well 

 supplied with available potassium results in the liberation of other 

 more deficient plant-food elements. Moreover, it may be applied to 

 soils having a large quantity of total potassium, but a small quantity 

 available to plants. Therefore, one of the problems which is con- 

 fronting the farmer is how to render available as needed by plants 

 the large supply of potassium in the soil. 



The potassium occurs in the soil mainly as silicates and is rendered 

 soluble by the nitrous, nitric, sulphuric, acetic, lactic, and butyric 

 acids, and by carbon dioxid. The last may react with inert potas- 

 sium resulting in the formation of available potassium according to 

 the following equation : 



A1 2 O 3 K 2 O. 6SiO 2 + CO 2 + 2H 2 O = A1 2 O 3 2SiO 2 + 2H 2 O + 



K 2 CO 3 + 4SiO 2 



Hence, the addition of animal manure, green manures, com- 

 mercial fertilizers, or even soil amendments may increase bacterial 

 activity and in a similar degree increase the soluble soil potassium. 



REFERENCES. 



Lafar, Franz: "Handbueh der Teohnischen Mykologie," Dritter Band. 

 Greaves, J. E., Carter, E. G.: "The Action of Some Common Soil Amendments" 

 (Soil Science, vol. vii (1919), pp. 121-160). 



Kossowicz, Alex.: "Agrikulturmykologie, I Bodenbakteriologie." 

 Ellis, David: Iron Bacteria, London, 1919. 



