vii.] MYCORHIZA 239 



and similar antiseptics is effective in restoring the soil 

 to its earlier capacity for dealing with the sewage. 



Though the experiments have as yet been tried on 

 but a small working scale, there will undoubtedly be a 

 valuable application in this direction of the antiseptic 

 that is being sought for to get rid of the protozoa in 

 ordinary cultivated soils, for by its means it will be 

 possible to deal with sewage on much smaller areas of 

 land than are now required for that purpose. 



Iron Bacteria. 



Another series of bacteria playing an interesting 

 part in certain soils, consists of those which secrete 

 hydrated ferric oxide or bog-iron ore in undrained soils, 

 where the soil water contains ferrous bicarbonate in 

 solution. Winogradsky investigated four of these 

 organisms, to whose vital processes he considered the 

 presence of soluble ferrous salts was essential. Molisch, 

 however, regards the secretion of ferric hydrate as, in 

 a sense, an accidental accompaniment of their growth, 

 much as the separation of large quantities of silica, so 

 characteristic of the straw of cereals, is unessential to 

 their development. It has already been noted that 

 these iron earths do not form in soils containing calcium 

 carbonate, which seems to prevent the formation of any 

 soluble ferrous compounds. 



Fungi of Importance in the Soil. 



Allusion has already been made to the fact that a 

 large number of fungi inhabit the soil Pcnicillium, 

 Mucor, Trichoderma y Spicaria, etc., Cladosporium, Clado- 

 tkrix, and various wild yeasts, Monilia, etc. all of 

 which aid in breaking down the organic matter. Many 

 of these fungi possess the power of attacking ammonium 

 salts applied as manure, withdrawing the ammonia and 



