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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 
form 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 
destroyed by an enzyme, or ferment, produced within the plant. 
The nitrogenous matter is dissolved and absorbed by the plant, and 
the nodules gradually diminish in size. 
In consequence of this power of leguminous plants to obtain sup- 
plies of nitrogen from the air, it is obvious that they are of much 
greater value for green manuring purposes than noil-leguminous 
crops, as apart from adding organic matter to the soil, their growth 
and subsequent ploughing-in are equivalent to the application of an 
expensive nitrogenous manure, such as sodium nitrate or sulphate 
of ammonia. 
It has been shewn that some soils, though capable of growing 
leguminous crops, are deficient in the specific organisms which 
enable these crops to assimilate nitrogen. As the result of a com- 
plete scientific investigation of the nature and mode of action of the 
organism, however, the U. S. Department of Agriculture now sup- 
ply pure cultures of the bacteria in question, by which the soil of 
any given field, or the seed about to be sown, may be inoculated 
with the nitrogen-fixing organism. It is stated in the Bulletin deal- 
ing with the above investigation that the following conclusions have 
been drawn, as the result of the observations made by the Depart- 
ment: Inoculation is not likely to produce any beneficial effect 
upon soils which already contain the necessary bacteria, or upon 
soils rich in nitrogen, or again upon soils which, on account of their 
acidity, are unsuitable for the growth of leguminous plants. Inocula- 
tion is undoubtedly of value where the bacteria do not already exist 
Bi-~ 1 1 
