LECT. V.] THE ROOT. SOILS. 219 



of vegetables. It is the oxygenous portion of the 

 atmospherical air contained in the soil, which is 

 vitiated by the functions of the roots of plants, I 

 shall have an opportunity of demonstrating to you 

 the importance of this agent in the process of 

 germination ; and Sir H. Davy concludes, from an 

 experiment on the vegetation of a Potatoe, in a 

 given portion of atmospherical air, at a tempera- 

 ture of 59',, " that in cases in which shoots are 

 thrown out from roots, oxygene appears to be 

 uniformly absorbed, as in the germination of 

 seeds* 1 ." Now, without stopping, at present, to 

 inquire whether the opinion that it is absorbed in 

 the process of germination be correct, it is evi- 

 dent that no accurate conclusions could be de- 

 duced from this experiment, because tubers per- 

 form nearly the same functions in evolving the 

 buds' on their surfaces, as the seed-lobes in the 

 evolution of the embryon they enclose, during 

 germination. To ascertain, therefore, the real 

 manner in which the functions of the living root 

 affect atmospherical air, I instituted the following 

 experiment: The roots of a Lilac, Syringa 

 vulgaris, were partly laid bare, and one of them 

 introduced into a cylindrical glass jar containing 

 atmospherical air, freed from carbonic acid, and 

 inverted in water. At the end of four days, du- 



* Elements of agricultural Chemistry, 2d edit. p. 233. 



