159 



nient and Avhicli ^vill cause their ci-ops continually to increase and 

 Avill finally enrich the soil to the extreme limit of its possible fei-tility. 



This would undoubtedly be a vast extension of that admiral)!e 

 humanitarian work for which we are indebted to Pasteur; but this 

 is anticipation, and I only proposed in this lecture to point out the 

 jjresent state of the question. I shall therefore close by sunnninjij 

 up what I have said in a few words. 



Experiments made by Ville, and repeated and \erified by many 

 other observers, have shown us that certain plants, i)articularly those 

 of the species of the Leg^uminosic. have taken iroin the atmosphere a 

 part of the nitrojren 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 shoAvn 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 Leguminosae. 



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 l»e followed had already been marked out l)y previous researches. 

 The problem was ripe for solution, and it was in our own country — 

 in France— that the great problem of the assimilation of nitrogen 

 had been proposed and in a great part solved, which is no more 

 than Avas to be expected from so great a center of production and 

 agri(;ultural progress. 



Professor Frank, of the agricultural institute in Berlin, finds that 

 the tul)ercles uuiy be removed from the plant without stopping the 

 ])r()cess of taking nitrogen from the air. Fvideiitly, therefore, the 

 subject has to be investigated still further. (Agr. Sci., Vol. lY, 

 p. 68.) 



Frank has also shown that the symbiosis in the tubercles of the 

 Leguminosa^ is of an entirely difi'erent 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. Sci., 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, (Jernuiny, along the line of investigation 

 conducted by Boussingault and Ville in France, Lawes and Gi.lbert 

 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 



