OF THE NITROGEN OF PLANTS. 91 



volume, after having been completely dried under 

 the air-pump. We have here an easy and 

 satisfactory means of explaining still further 

 the properties of humus, or wood in a decaying 

 state. It is not only a slow and constant source 

 of carbonic acid, but it is also a means by 

 which the necessary nitrogen is conveyed to 

 plants. 



Nitrogen is found in lichens, which grow on 

 basaltic rocks. Our fields produce more of it than 

 we have given them as manure, and it exists in all 

 kinds of soils and minerals which were never in 

 contact with organic substances. The nitrogen in 

 these cases could only have been extracted from the 

 atmosphere. 



We find this nitrogen in the atmosphere in rain- 

 water and in all kinds of soils, in the form of am- 

 monia, as a product of the decay and putrefaction 

 of preceding generations of animals and vegetables. 

 We find likewise that the proportion of azotised 

 matters in plants is augmented by giving them a 

 larger supply of ammonia conveyed in the form of 

 animal manure. 



No conclusion can then have a better foundation 

 than this, that it is the ammonia of the atmosphere 

 which furnishes nitrogen to plants. 



Carbonic acid, water and ammonia, contain the 

 elements necessary for the support of animals and 

 vegetables. The same substances are the ultimate 

 products of the chemical processes of decay and 



