CONCLUSION. 5? 



a means by which the necessary nitrogen is conveyed to 

 plants.* 



Nitrogen is found in lichens growing 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 ammonia, 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 nitro- 

 gen 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 putrefaction. All the innumerable products of 

 vitality, resume, after death, the original form from which they 

 sprung. 



Thus the destruction of an existing generation becomes the 

 means for the production of a new one, and death becomes the 

 source of life. 



But it may be asked — Are the compounds now named the 

 only substances necessary- for the support of vegetable life ? This 

 question must be answered decidedly in the negative. 



* When the extract of humus is evaporated with muriatic acid, a residue 

 is obtained which evolves ammonia by the addition of potash. When this 

 extract is subjected to distillation along with water, and the products of 

 distillation received into dilute muriatic acid, the latter is found to contain 

 muriate of ammonia. Humus contains carbonate of ammonia. — Wieg- 

 mann und Polstorf, Priesschrift, s. 53. 



t We refer the reader to the Appendix for the part which nitric acid 

 takes in vegetation, and also for the origin of ammonia 

 4* 



