70 now CROPS FEED. 



ozone actually produced iu tlie atraos2)herc and consumed 

 in it, or at tiie surface of the soil. We have as yet indeed 

 no satisfactory means of information on this point, but 

 may safely conclude from the foregoing considerations that 

 ozone performs an important part in the economy of 

 nature. 

 Relations of Ozone to Vegetable lAutrition. — Of the 



direct influence of atmospheric ozone on plants, nothing 

 is certainly known. Theoretically it should be consumed 

 by them in various processes of oxidation, and would have 

 ultimately the same eiFects that are produced by ordinary 

 oxygen. 



Indirectly, ozone is of great significance in our theory 

 of vegetable iiutiition, inasmuch as it is the cause of chem- 

 ical changes which are of the highest importance in main- 

 taining tlie life of ])lants. This fact will appear in the 

 section on Nitric Acid, which follows. 



§ 8- 



COMPOUNDS OF NITROGEN AND OXYGEN IN THE ATMOS- 

 PHERE. 



Nitric Acid, NO3H. — Under the more common name 

 Aqua fortls (strong water) this highly important sub- 

 stance is to be found in every apothecary shop. It is, 

 when pure, a coloi-less, usually a yellow liquid, whose 

 most obvious properties are its sour, burning taste, and 

 power of dissolving, or acting upon, many metals and other 

 bodies. 



When pure, it is a half heavier than its own bulk of 

 water, and emits pungent, suffocating vapors or fumes ; in 

 this state it is rarely seen, being -in general mixed or di- 

 luted with more or less Avater ; when very dilute, it evolves 

 no fumes, and is even pleasant to the taste. 



It has the properties of an acid in the most eminent de- 

 gree; vegetable blue colors are reddened by it, and it 



