159 
ment and which will cause their crops continually to increase and 
will finally enrich the soil to the extreme limit of its possible fertility. 
This would undoubtedly be a vast extension of that admirable 
humanitarian work for which we are indebted to Pasteur; but this 
is anticipation, and I only proposed in-this lecture to point cut the 
present state of the question. I shall therefore close by summing 
up what I have said in a few words. 
Experiments made by Ville, and repeated and verified by many 
other observers, have shown us that certain plants, particularly those 
of the species of the Leguminose, have taken from the atmosphere a 
part of the nitrogen that they contain. 
Berthelot, and also Gautier and Drouin, have shown that the soil 
alone can to a slight extent enrich itself by means also of a direct 
fixation of gaseous nitrogen. 
Berthelot has also shown that this phenomenon corresponds with 
the development of certain microbes preexisting in the soil; and, 
finally, Hellriegel and Wilfarth have discovered this micro-organism 
in the nodules on the roots of the Leguminosee. 
This last work is certainly one of the greatest interest, and does 
the greatest honor to the physiologists who have succeeded in bring- 
ing it to a final result; but it is proper to recognize that the route 
to be followed had already been marked out by previous researches. 
The problem was ripe for solution, and it was in our own country— 
m France—that the great problem of the assimilation of nitrogen 
had been proposed and in a great part solved, which is no more 
than was to be expected from so great a center of production and 
agricultural progress. : 
Professor Frank, of the agricultural institute in Berlin, finds that 
the tubercles may be removed from the plant without stopping the 
process of taking nitrogen from the air. Evidently, therefore, the 
subject has to be investigated still further. (Agr. Sci., Vol. IV, 
p- 68.) 
Frank has also shown that the symbiosis in the tubercles of the 
Leguminose is of an entirely different character from that which 
occurs in the roots of any other plants. Furthermore, when the 
soil is rich in humus the microbic parasite does no special service to 
the host, but when the supply of humus is insufficient the microbe 
symbiont is of the greatest service to the host. (Agr. Sei., Vol. IV, 
p- 266.) 
H. J. Wheeler, of the Rhode Island Experiment Station, gives 
(Agr. Sci., Vol. IV, p. 55) an account of the work done by Professor 
Hellriegel at Bernburg, Germany, along the line of investigation 
conducted by Boussingault and Ville in France, Lawes and Gilbert 
in England, and W. O. Atwater, of the Storrs School Agricultural 
Experiment Station. In the present state of the question it may be 
considered as settled that certain plants are able, if supplied with 
all the other essential elements, to draw their supply of nitrogen from 
