514 Dawson . — On the Economic 
weight of the crops obtained. During the course of these 
experiments over 800 plants have been under investigation 
in this manner. 
With regard to the relative weights of the crops the results 
showed that on ordinary garden soil, on sand, and on sand 
manured with nitrate, inoculation with ‘Nitragin’ is accom- 
panied by a loss of weight in the crop, but that a small 
increase is secured on gravelly subsoil. 
In sand-grown plants a considerable increase in the crop 
was produced by a supply of nitrates alone, but inoculation 
with ‘Nitragin’ in the presence of a sufficient supply of 
nitrogenous food, whether in the form of humus or of potas- 
sium nitrate, is not beneficial. 
This set of experiments also showed clearly the extreme 
difficulty of securing sterile conditions in the culture-soils for 
a considerable period of time, and emphasized the fact of the 
undoubted ubiquity of the nodule-organisms in air and soils 
alike ; for, in spite of the greatest care in all manipulations 
to prevent chance infection of the roots, nodules were fre- 
quently found on the roots of control-plants. It is scarcely 
possible that this was due to incomplete sterilization of the 
soils, for I have repeatedly grown peas and other Leguminous 
plants on media, treated in a similar manner for a period not 
exceeding six weeks, without any trace of infection. In 
addition, it should be pointed out that the nodules, when 
present on control-plants, were always fewer in number, 
smaller and more crowded together than those borne by 
plants inoculated with ‘Nitragin.’ Moreover the frequent 
occurrence of the fructification of Peziza confluens on these 
sterilized media shows how easily air-borne germs could be 
introduced. It would seem therefore that these nodule- 
organisms must be regarded as amongst the most ubiquitous 
of known organisms and, like those of putrefaction and fer- 
mentation, extremely difficult to remove with certainty for 
a considerable length of time. At one stage in the experi- 
ments it was observed that though no very appreciable 
difference could be detected between the vegetative organs 
