335 



cultivated soil was added, the plants recovered, formed nodules on 

 the roots, and also became capable of absorbing nitrogen. These 

 nodules, upon examination, were found to be full of organisms which, 

 since the sand in which the plants were growing had been sterilized, 

 could only have been derived from the water extract of the cultivated 

 soil that had been added. It was concluded from these observations 

 that the assimilation of free nitrogen by leguminous plants takes 

 place after the formation of root nodules, which are caused by some 

 organism present in cultivated soil. 



These organisms have been isolated, and further observation has 

 shewn that the different forms associated with different leguminous 

 plants are all modifications of one species, to which the name, 

 Pseudomonas radicicola, Beyerinck, has been assigned. 



As regards the actual way in which the bacterial organism enables 

 the plant to assimilate nitrogen from the atmosphere, since it has 

 been proved that the organism itself, even when isolated from the 

 plant nodule, can in certain forms, take up nitrogen, and store it up 

 in itself as nitrogenous matter, there seems little doubt that it also 

 absorbs nitrogen in this way when in the nodule. 



The present view of the case, briefly stated, is that, firstly, the 

 bacterium enters the root of the plant, where its originally minute 

 torm changes into a rod-like shape, multiplies, assimilates 'nitrogen, 

 and stores up nitrogenous compounds, and then finally, in the nodule, 

 the rod-like form changes to the branched form, which is ultimately 

 Oestroyed by an enzyme, or ferment, produced within the plant, 

 ine nitrogenous matter is dissolved and absorbed by the plant, and 

 the nodules gradually diminish in size. 



Jn consequence of this power of leguminous plants to obtain sup- 

 pies of nitrogen from the air, it is obvious that they are of much 

 greater value for green manuring purposes than non-leguminous 

 and u S apart from addin g organic matter to the soil, their growth 

 " su ?sequent ploughing-in are equivalent to the application of an 



Pensive nitrogenous manure, such as sodium nitrate or sulphate 

 01 ammonia. 



It has been shewn that some soils, though capable of growing 

 juminous crops, are deficient in the specific organisms which 

 ' "'ate nitrogen. As the result of a com- 

 stigation of the nature and mode of action of the 

 piv7 Sm ' howeve r, the U. S. Department of Agriculture now sup- 

 ^ Pure cultures of the bacteria in question, by which the soil of 

 with tk • eld ' orthe seed about to be sovvn, maybe inoculated 

 i n . J£, e ^ogen-fixing organism. It is stated in the Bulletin deal- 

 been H above investigation that the following conclusions have 

 Rient T Vn ' as the result of the observations made by the Depart- 

 W^-i lation is not likel y to produce any beneficial effect 

 ^ikh ' HlCh alread y contain the necessary bacteria, or upon 

 acidi tv C m n,tro g en , or again upon soils which, on account of their 

 ti 0n is y ' are unsuitable for the growth of leguminous plants. Inocula- 

 u naoubtedly of value where the bacteria do not already exist 



