liebig's mineral theoey. 119 



applied to the soil, would be as effective in pro- 

 moting the growth of the crop as if supplied in the 

 ordinary manner. 



This theory, so cleverly stated by such an emi- 

 nent authority, attracted immediate and widespread 

 attention. Chemists engaged at once in the analy- 

 sis of soils to determine what they contained, and 

 in the analysis of plants to determine what they 

 required. There appeared to be no flaw in the 

 theory, and a new era of prosperity seemed about 

 to open upon agriculture. Large establishments 

 were erected for the manufacture of wheat manure, 

 barley manure, turnip manure, etc., each adapted 

 to the needs of the particular crop. But when 

 these manures came to be tried in the field the 

 result was a disastrous failure. We now know 

 that there was a flaw in the theory, that if plants 

 do not take up carbon from the soil they do obtain 

 nitrogen mainly from the soil instead of from the 

 air, and that the presence of decaying vegetable 

 matter enables soils to withdraw from the air 

 supplies of the much needed nitrogen for the use 

 of plants. It is only recently that we have learned 

 how the presence of organic matter enables the 

 soil to accumulate the nitrogen upon which the 

 plants may feed. It is only during the decay or 

 fermentation of this organic matter through the 

 agency of bacteria that this valuable material is 



