692 The Sources of the Nitrogen of our Leguminous Crops. 
the roots. In the other cases of gain no mention is made of 
tubercles, and it may be that the roots wei'e not so examined as 
to determine whether they existed or not. It is, at any rate, 
very significant, when viewed in the light of recently acquired 
knowledge, that in all the cases of gain the plants grown were 
of the leguminous family, and that in some of them nodules 
were observed on the roots. 
Again, Berthelot's experiments showed fixation of free nitro- 
gen by the agency of microbes within the soil, both in the 
absence of higher vegetation, and also coincidently with the 
growth of non-leguminous plants. He further considers that 
such fixation takes place to an extent which would be an im- 
portant source of nitrogen to our crops. As referred to above, 
Boussingault's experiments of 1858 and 1859 showed fixation 
within the soil which he then attributed to the agency of myco- 
dermic vegetation. The fact of such fixation within the soil, 
under the influence of lower plants, has also been confirmed by the 
recent results of some other experimenters. Thus, MM. Schloesing 
fils and Laurent have shown fixation in bare soil, and in soils 
growing various non-leguminous plants, when certain Lichens 
and Algae were developed, but not when their occurrence was 
prevented. We believe that Hellriegel has also found fixation 
coincidently with the growth of certain Algse. Nevertheless, it 
may be observed, that neither experience in practical agriculture, 
nor the nitrogen statistics of soils and crops, points to the conclu- 
sion that there is gain of nitrogen to any material extent by the 
fixation of free nitrogen under the agency of microbes within 
the soil independently of leguminous growth. It was our in- 
tention to commence experiments on this subject at Rothamsted 
in the past year (1891), but we have not yet been able to do so. 
In 1888, however, Berthelot made numerous experiments 
with Ijeguviinosa', and in many of them he found very large 
gains of nitrogen ; indeed, a much higher range of gain than in 
his other experiments. That there should be large gain under 
such conditions is quite consistent with the results which have 
been recorded of the experiments made at Rothamsted in 1888 
and 1889 with Legmninosa' , and with those previously obtained 
by Hellriegel and AVilfarth. Further, these results of Berthelot, 
like those obtained at Rothamsted and by others with legumin- 
ous plants, are consistent with well-established facts of agricul- 
tural production, and with the nitrogen statistics of soils and 
crops, and serve with them to aid the solution of long-recog- 
nised problems in connection with the growth of leguminous 
crops. 
But, whether or not it may eventually be established that 
