182 



For finding out the value per ton the certificate is treated just tli^ 

 fiame as an invoice, except that, instead of dealing with lbs. of materi- 

 als at certain prices, one has to deal with percentages at certain values. 

 Thus, if 1 per cent, of nitrogen in a ton of manure were worth 12s., 

 5 per cent, would be worth 60s. The value of 1 per cent, of an ingre- 

 dient in a ton of manure is called the unit value. These unit values 

 change according to changes in the manure market, but they remain 

 fairly constant during ( ne season. 



''Manures and Manuring" By A. H. Pearson, Chemist to the Depart-- 

 ment of Agriculture, Victoria. 



NITROGEN-FIXING BACTERIA. * 



Besides the nitrifying bacteria which are able to transfer ammonium^ 

 ealts found naturally in soil, or have been added thereto, into other 

 nitrogenous compounds, a number of related organisms are met with 

 in many fields which have the power of utilising the free nitrogen of 

 the atmosphere and drawing from this vast store of almost inert gas 

 considerable quantities for plant food. These are the nitrogen-fixing 

 bacteria. 



On the rootlets of many higher plants, more especially on those of tbe 

 ZegtmuiosWj smtjll nodules in varying numbers are found produced by 

 and filled with bacteria. It is supposed that by the symbiosis (a 

 living together) of these lowest forms of plant-life with the higher 

 plants, the latter derive the nitrogenous food which it is proved can- 

 not have been derived from the soil, and therefore must have been 

 obtained from the aimosphere. The process is not yet properly un- 

 derstood but the general opinion tends towards the assumption that 

 the bacteria fix the free nitrogen within the nodules and that the 

 resulting nitrogenous compounds are assimilated by the host-plant. 



By some also it is thought that through the peculiar conditions 

 of " living together" the plant is enabled to fix free nitrogen in its 

 foliage. 



"Whatever may be the correct theory, the effect of this remarkable 

 interaction between the low forms and the higher plants is very strik- 

 ing and very variable in extent. Even amongst tha Leguminosce, the 

 plants deriving the greatest advantage from this phenomenon, extremes 

 are met with; some deriving apparently but little benefit from it, 

 whilst on the other hand many may very largely depend upon it, 

 .Amongst the Lupines, for instance, the yellow flowering variety is 

 able to entirely dispense with nitrogenous substances in the soil. 



Through the exhaustive investigations made first by Professors 

 Hallriegel and Wilfarth, and later by Lawes, Gilbert, and others, on 

 nearly all the cultivated leguminous plants, no doubt has been left 

 that the nodules found on the roots are formed through bacteria, and 

 that these are able to fix in e nitrogen for the use of the plant they 

 attach themselves to. Until Hallriegel proved that the presence of 



> * Extract from a Paper on " Soil Bacteria" by R. Helms, in the " AgriculturaL 



. ' Gazette" of New South Wales, for July, 19uO. 



