516 Dawson . — On the Economic 
As regards the relative weights of the crops, an increase as 
the result of inoculation was observed on the gravelly subsoil 
only, and even here the increase was but small ; on peat, clay, 
loam or ordinary garden-soil, on the contrary, inoculation 
with ‘ Nitragin ’ proved to be both useless and superfluous. 
In the report of the work undertaken during the year 1897, 
in the various experimental stations of Prussia \ accounts are 
given of the use of ‘Nitragin’ with different genera of the 
Leguminosae and on soils of different characters. In general 
the results show that the artificially cultivated organisms are 
either quite useless for infection or superfluous. On some 
soils, e. g. sandy heaths and moorland, it was found that 
inoculation with soils known to contain the organisms in 
question was more beneficial to the crops than the use of the 
pure culture, ‘ Nitragin.’ 
Frank 1 2 , in a discussion of these results, suggests that the 
failure of c Nitragin ’ as an agricultural fertilizer of Leguminous 
crops may be due to a change of properties having been 
induced in the organisms by artificial cultivation, which change 
has lessened their virulence, and consequent action within the 
host-plants. He concludes from these facts that a more suit- 
able culture-medium should be adopted in order to keep the 
properties of the organisms unchanged. It is to be noticed, 
however, that this author has not suggested of what this new 
medium should consist. Nobbe and Hiltner 3 hold the view 
that this loss of virulence is due to the same nutrient gelatine 
being used in each case, whatever the organism cultivated, 
e. g. Lupinus organisms on pea-extract gelatine. 
They consider that the special adaptation of the c bacteria ’ 
to each host is dependent upon the presence of different food 
materials within each host. According to these authors the 
value of nodules to the Leguminous plant is in direct propor- 
1 Landwirthsch. Jahrb., 1898, Band XXVIII. 
2 Frank, ‘ Die bisher erzielten Ergebnisse der Nitraginimpfung.’ Landwirthsch. 
Versuchsst., 1899. 
3 Nobbe and Hiltner, ‘Wie lasst sich die Wirkung des Nitragins erhohen?’ 
Landwirthsch. Versuchsst., 1899. 
