13 



connection with these plants is the fact that when they 

 have yielded their crop they have not exhausted the soil 

 o^ its nitrogen compounds, but will be found to have 

 actually enriched it. This renders leguminous plants a 

 valuable crop to alternate with other crops which deplete 

 the soil of nitrogenous material. In agriculture it is often 

 found expedient in the case of poor or exhausted fields to 

 dig in a leguminous crop such as lupins or clover, which 

 are often grown for the, purpose of enriching the soil. 



With a view to increasing the number of the nitrify- 

 ing organisms in the soil attempts have been made in this 

 and other countries to introduce more of these bacteria, 

 particularly into pots or beds in which sweet peas or other 

 members of that family are to be grown. In England 

 preparations of these bacteria were distributed some years 

 ago as " nitrobacterine,'' but the use of this preparation 

 was not found profitable ni all cases, probablv as in many 

 soils there is already a sufficient supply of these bacteria. 

 Professor Bottomley has, however, now^ discovered a better 

 way of cultivating these bacteria in peat, with which they 

 can be easily distributed. Peat, which represents the 

 partially decayed vegetable remains, differs from leaf 

 mould or humus in undergoing decay under very w^et con- 

 ditions. As a consequence it remains permeated with 

 certain substances which render it acid and unsuited to the 

 growth of most plants, though heaths, azaleas, rhododen- 

 drons, and other members of the heather family grow 

 well in peaty soil. When rendered alcaline, however, peat 

 has been found to favour the development of roots, and 

 therefore the whole growth of plants, and containing as it 

 does a large amount of organic material, much of which 

 is rendered soluble when alcaline, it has a high manurial 

 value. This is said to be still further increased by inocu- 

 lating the peat with nitrifying bacteria, which grow very 

 vigorously in alcaline peat and thus increase the available 

 plant foods. Bacterised peat," as it is called, is not yet 

 on the market, and has therefore not been extensively 

 tried, but experiments which have been conducted at Kew 

 Gardens with pot plants, and on a farm near Norwich, are 

 of considerable promiise.^ 



* ^' The Spirit of the Soil.^' An account of the nitrogen fixation 

 in the soil by bacteria, and of the production of auximones as 

 promoted by bacterised peat. By G. D. Knox. Constable. 

 London, 1015. 



