Science progress. 



No. 16. June, 1895. Vol. III. 



NEW ASPECTS OF AN OLD AGRICULTURAL 



QUESTION. 



THE FIXATION OF FREE NITROGEN BY PLANTS. 



PROBABLY no question in the history of agriculture 

 has stirred the mind of man more than that which 

 asks : " Whence do plants obtain their nitrogen ? " And of 

 late years, when science had apparently succeeded in giving 

 a very definite and complete answer to the question as 

 regards most plants, and in showing that the question itself 

 raises a number of others which must be attacked separately 

 before we can hope for the answer as regards others, a gradu- 

 ally culminating storm directed on what appeared to be the 

 last stronghold to be conquered has been slowly organised 

 from various directions, and brought about a conflagration 

 of hypotheses and suggestions which promises not only to 

 break down or blow up the citadel in question, but to light 

 up the territory around so brilliantly, and from so many sides, 

 that its aspect will be entirely changed. From the ruins of 

 the old ideas the new agriculture will arise. 



We are told (2) that the Romans were aware of the 

 fact that impoverished agricultural land could be enriched 

 by growing beans, lucerne, and other papilionaceous plants 

 on it for a season, and that the addition of manure was not 

 necessary ; and it is evident that a belief in the efficacy of 

 certain crops as soil improvers has prevailed at various 

 times in different countries. 



It is clear, however, that no definite ideas of import- 



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