146 SOILS AND. MANURES 



the air, consider that a light dressing of nitrogenous, 

 manure is highly beneficial to these crops. 



The Seat of Fixation. The seat of fixation of the 

 nitrogen has been a matter of some dispute. Some 

 observers have declared it to be in the leaves and others 

 in the root of the leguminous plant, but there appears to 

 be little room for doubt that it is in the nodules themselves 

 that fixation actually takes place. It has been found that 

 the process is arrested when the nodules are submerged 

 in water. The nodular cells are in communication with 

 those of the root proper by a regular system of conducting 

 vessels, and they exhibit signs of intense metabolic activity. 

 There is thus, apparently, a true organic union between 

 the bacteria and the higher plant, and the opinion is widely 

 held, if not universally accepted, that the stimulating effect 

 of the symbiotic association is the true cause of fixation. 



Inoculation of Soils. The discovery of the fixation of 

 free nitrogen by leguminous plants and the cause thereof 

 naturally gave rise to somewhat inflated ideas as to the 

 practical benefits likely to be derived from it. It was 

 anticipated that by inoculating the soil with bacteria, 

 larger crops would be obtained, a remedy would be found 

 for clover sickness, and that it might become possible to 

 grow leguminous crops on soils hitherto regarded as not 

 naturally well adapted for the purpose. The method of 

 inoculation first proposed was to top dress the land with 

 soil taken from another field on which leguminous crops 

 were known to flourish. A great many experiments on 

 these lines have been tried, and some of them gave positive 

 results. Those with which the writer was concerned did 

 not. Subsequent investigations have shown that though a 

 certain improvement may sometimes be effected in this 

 way, the beneficial effects are, as a rule, too small to be 

 of practical importance. 



Later it was claimed that the bacillus radicicola the 



