On the Economic Importance of ‘ Nitragin.’ 
BY 
MARIA DAWSON, D.Sc. (Lond. and Wales), 
Late 1851 Exhibition Science Research Scholar. 
I N connexion with the comparatively recent rise of Agri- 
culture as a practical science, there is perhaps no more 
important question than the supply of an adequate quantity 
of suitable nitrogenous food to plants, from which has arisen 
the study of the part played by the innumerable micro- 
organisms of the soil and air in the regulation of this supply, 
both quantitatively and qualitatively. 
The special interest of the Leguminosae in this connexion 
has been recognized ever since the classical researches of 
Boussingault, and from that time there has been an unbroken 
series of investigations — in particular those of Lawes, Gilbert, 
and Pugh in England and Hellriegel and Wilfarth in Germany — 
upon the phenomena involved in the increased nitrogen con- 
tent of the soil, found to be a constant result of the cultivation 
of a Leguminous crop. The first important stage towards 
the explanation of these phenomena was reached by the 
determination that this increase in nitrogen was directly 
correlated with the presence upon the roots of the Legu- 
minous plants of nodules, which owed their formation to 
the action of parasitic micro-organisms present in the soil. 
Beyerincks discovery that the organisms were capable of 
growth on nutrient media, outside the plant, and that they 
could be obtained direct from the culture-soils, led to very 
[Annals of Botany, Vol. XV. No. LIX. September, 1901.] 
