176 NITROGEN. 



" The most abundant product of tlie decay of veg- 

 etable matter in the soil is this same gas. In land 

 replete with vegetable matter, therefore, the roots 

 are surrounded by an atmosphere more or less 

 charged with it. Hence, if they are capable of in- 

 haling gaseous substances, this will enter the roots 

 in the aeriform state ; if not, it must enter in solu- 

 tion. 



4. Nitrogen. " The question as to the form in 

 w^hich nitrogen enters the circulation of plants, at 

 the present moment engages much attention. 



" It is considered an essential part of good tillage 

 to break up and loosen the soil, in order that the 

 air may have access to the dead vegetable matter, 

 as well as to the living roots, which descend to 

 considerable depths beneath the surface. When 

 thus admitted to the roots, some of the nitrogen of 

 the atmosphere, as well as a portion of its oxygen, 

 will undoubtedly be directly absorbed and appro- 

 priated by the plant. To what extent this absorp- 

 tion of nitrogen may proceed we have as yet no 

 experimental results from which we can form an 

 estimate ; — whether it takes place at all or not, is 

 wholly a matter of opinion. 



" The leaves of plants absorb certain gaseous sub- 

 stances from the atmosphere, and we might there- 

 fore expect that some of the nitrogen of the atmos- 

 phere would by this means be admitted to their 

 circulation. This view is not confirmed by any of 



