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 poses the nitrogen of the atmosphere to combine 

 with the plants. But, before speaking deci- 

 sively as to this explanation, it must be ascer- 

 tained whether the nitrate of ammonia can 

 really contribute to the production of the nitro- 

 genous principles met with in all the plants.'' 



More recently Boussingault has added, that 

 "the nitrogen can enter directly into the or- 

 ganism of plants if their green parts are quali- 

 fied for its fixation : it can also be carried into 

 plants by the water (always aerated) which is 

 imbibed by their roots. Indeed, some philo- 

 sophers are of opinion that the atmosphere 

 probably contains an infinitely small quantity 

 of ammoniacal vapours." 



Liebig is of the opinion, that this excess of 

 nitrogen proceeds from the ammonia imbibed 

 by the plants from the atmosphere wherein it 

 is found, but in such minute quantities that the 

 most delicate tests frequently fail to detect its 

 presence. 



The nitrogen of the air is, in most cases, far 

 from sufficient for the complete growth of 

 plants, or at least for the production of an abun- 

 dant harvest. Most agriculturists even believe 

 that many entire families of plants, as the 

 gramineals, are incapable of assimilating it. 



