ABSORPTION OF AQUEOUS VAPOR. 151 



plants derive from oxygen gas applied to their roots. 

 This is another reason for increasing the moisture 

 of the soil by deep and complete ploughings ; for 

 M. Humboldt and M. Schubler have clearly shown 

 that a dry soil is quite incapable of absorbing 

 oxygen gas. Thus it must be evident to the most 

 listless observer that the deeper and more thoroughly 

 a soil is pulverized, and its earth made permeable, 

 the greater will be the absorption by it of both 

 oxygen and watery vapor from the surrounding 

 atmosphere. 



" It is, perhaps, needless to prove that the roots 

 of most cultivated plants will penetrate, under favor- 

 able circumstances, to a much greater depth in 

 search of moisture than they usually do, on account 

 of the hardened subsoil. Thus, the roots of the 

 wheat plant in loose, deep soils have been found to 

 descend to a depth of two or three feet, or even 

 more. It is evident, if plants are principally sus- 

 tained in dry weather by the atmospheric aqueous 

 vapor absorbed by the soil, that at such a time their 

 supply of water at the roots must be increased, by 

 enabling the atmospheric vapor and gases, as well 

 as the roots of plants, to attain a greater depth ; for 

 the interior of a well-pulverized soil, be it remem- 

 bered, continues steadily to absorb this essential 

 food of vegetables even when the surface of the 

 earth is drying in the sun. The free access of air 

 to the soil adds to its fertility, by promoting the 

 decomposition of organic substances in it." 



