The Sources of the Nitrogen of our Leguminous Crufis. G65 
sterilisation there was no such result. Consistent results were 
obtained with peas, vetches, and some other Leguminosca ; but 
the application of the same soil-extract had little or no effect, 
in the case of lupins, serradella, and some other plants of the 
family, which are known to grow more naturally on sandy than 
on loamy or rich humus soils. Accordingly, they made a similar 
extract from a diluvial sandy soil, where lupins were growing 
well, in which it might be supposed that the organism peculiar 
to such a soil would be present ; and, on the application of this 
to a nitrogen- free soil, lupins grew in it luxuriantly, and nodules 
were abundantly developed on their roots. 
Further particulars of the experiments of Hellriegel and 
Wilfarth, and also of the results and conclusions of Berthelot, 
Deherain, Joulie, Dietzell, Frank, Emil von Wolff, and Atwater, 
as well as of some of the later experiments of Boussingault 
which have a bearing on the present aspect of the question, will 
be found in our paper in the Philosophical Transactions, Vol. 180 
(1889), B. A short account is also given of the experiments 
of Breal, confirming the results of Hellriegel, in our paper in 
the " Proceedings of the Royal Society," Vol. 47, 1890. 
Thus, then, not only did Hellriegel and Wilfarth get nega- 
tive results with plants of other families than the Leguminosce, as 
all experience would lead us to expect, but they obtained posi- 
tive results with the Leguminosce, in regard to the source of the 
whole of the nitrogen of which experience showed that there 
was a " missing link." Such results were obviously of funda- 
mental and of far-reaching importance ; and it seemed desirable 
that the subject should be further investigated with a view to 
their confirmation or otherwise. Accordingly, it was decided to 
take it up at Rothamsted, and it was hoped to commence experi- 
ments in 1887, but it was not possible to do so until 1888. In 
that year, a preliminary series was undertaken ; the investigation 
was continued in 1889 and 1890, and is, in fact, still in progress. 
It is proposed to give in the following pages some account 
of the conditions and of the results of these recent experiments 
made at Rothamsted, which do show a fixation of free nitrogen. 
But, before doing so, it will be well to call attention to those of 
the earlier experiments, which did not indicate any fixation ; as 
the well-defined diSereuce in the conditions under which such 
difierent results were obtained will bring clearly to view what 
are the conditions under which fixation does, and what are those 
under which it does not, take place. We shall thus, too, be the 
better able to form some judgmerit as to the practical bearing 
of the receut results, 
