UTILIZATION OF ATMOSPHERIC NITROGEN Si 



acting in symbiosis with leguminosae. These organisms enter 

 the plant by first attacking the root hair, and a filament 

 gradually extends up into the root, where the nodule begins 

 to form ; but beyond this the organisms do not penetrate. The 

 organisms soon surround themselves with slime, and appear 

 as bacterial rods. The organisms only enter, in any quantity, 

 the particular species of plant to which they are accustomed, 

 but they can be trained to attack other species, although 

 they then lose the power of attacking their original hosts. 



The process of the fixation of nitrogen by bacteria can be 

 worked artificially. Leguminous plants can be made to 

 grow perfectly without organisms by means of feeding with 

 nitrogenous compounds. On the other hand, the organisms 

 can be grown on artificial media containing carbohydrates, 

 nitrogen being obtained from the air. The fixation of nitro- 

 gen soon ceases unless the resulting compounds are removed ; 

 Golding has attained this end by an ingenious filtering device, 

 and has succeeded in fixing considerable quantities of nitrogen. 

 Nitrogen fixation is known to take place in the nodule, which 

 becomes richer in nitrogen than the rest of the plant, and it 

 is assumed that the final product is a soluble protein which 

 is passed on to the plant. 



At Rothamsted experiments show that where no clover 

 was grown barley produced 37 pounds of nitrogen per acre 

 in the crop, but where clover was grown with the barley the 

 amount of nitrogen in the crop was 151 pounds. The nitro- 

 gen left in the soil was 0*142 % where there was no clover, and 

 0*152 % where clover was grown. Similar results have been 

 obtained at Cockle Park, where, by treatment with basic 

 slag, land has steadily accumulated nitrogen. The plot 

 which received no manure decreased in its nitrogen content 

 from 0*197 to 0*174 % in seventeen years' time, but the plot 

 that was treated with basic slag rose in nitrogen content from 

 0*227 to 0*244 % in eight years' time. With the presence of 

 the basic slag, the organisms had been able to develop and fix 

 nitrogen in the soil in considerable quantities, but without 

 proper manuring they had been unable to keep pace with 

 the inevitable losses by drainage. 



v. 6 



