92 CHYMISTRY APPLIED TO AGRICULTURE. 



hydrogen ; which appears to be furnished, in a great meas- 

 ure, by their power of decomposing water. Hydrogen can 

 be obtained from plapts by distillation, but in the decompo- 

 sition of dead vegetables, it unites either with the oxygen 

 of the air to form water, or it is exhaled in union with car- 

 bon as carburetted hydrogen. 



ARTICLE V. 



Of the Effects of the Nourishment of Plants upon the 

 Soil 



It appears to be clearly proved, that plants imbibe from 

 water and the atmosphere only carbon, oxygen, and hydro- 

 gen ; but analysis shows us that, independently of these 

 principles and the products arising from their combinations, 

 plants contain azote and some earthy and saline substances, 

 which cannot be produced by either of the three elements 

 mentioned above. It remains then for us to inquire, in 

 what manner these substances have been introduced into 

 plants. 



Azote, which is found in the albumen, the gelatine, and 

 the green coloring matter, is not sensibly drawn from the 

 atmosphere, though it constitutes f of it, but passes in with 

 oxygen in the water imbibed by plants, and, like that, is 

 separated in their organs. 



The earths which are insoluble in water, but which are 

 mixed with, or suspended in that fluid, are not absorbed in 

 large quantities by the pores of plants, but may be conveyed 

 into them by the aid of some chymical agents, as the acids, 

 the alkalies, &c. Besides, if we observe attentively, we 

 shall find that these substances do not abound in plants ; 

 and we can easily conceive, that the little they do contain, 

 might, in a state of extreme division, be introduced by 

 water. 



There are some plants that fasten themselves and grow 

 upon the most barren rocks, deriving from the surrounding 

 air, and from rains, all the nourishment required by them ; 

 of this number are the mosses, the lichens, and the fleshy 

 plants. Their growth is slow, their transpiration almost 

 nothingj» and their color remains nearly the same all the 



