22 now CROPS FEED. 



cur or may occur in tlie air in minute and variable quanti- 

 ties, viz. : 



Water, as vapor. . .average proportion by weight, ' l,oo 



Carbonic acid gas " " " " •|io-ooo 



Ammonia " " " " ' Iso- ooo- ooo ? 



' Ozone " " " «' minute traces. 



Nitric acid " " '< " " " 



Nitrons acid " " " " *' «' 



Marsh gas " " »' " " " 



In air of (^'^'■'^""''^''^i^^' " " " " 



-< Siili>liurous acid, " " " " *' " 



towns. ( g„ij,i,^^.(i,.j(. acid " " " " " " 



Miller gives for the air of England the following aver- 

 age proportions by volume of the four most abundant in- 

 gredients. — {Elements of Chemistry^ part II., p. 30, 3d Ed.) 



Oxygen 20.61 



Nitrogen 77.95 



Carbonic acid 04 



Water- vapor 1.40 



100.00 

 We may now appropriately proceed to notice in order 

 each of the ingredients of the atmosphere in reference to 

 the question of vegetable nutrition. This is a subject re- 

 garding which unaided observation can teach us little or 

 nothing. The atmosphere is so intangible to the senses 

 that, without some finer instruments of investigation, we 

 should forever be in ignorance, even of the separate exist- 

 ence of its two principal elements. Chemistry lias, how- 

 ever, set forth in a clear light many remarkable relations 

 of the Atmosphere to the Plant, whose study forms one 

 of the most instructive chapters of science. 



RELATIONS OF OXYGEN GAS TO VEGETABLE NUTRITION. 



Absorption of Oxygen Essential to Growtli,— The ele- 

 ment Oxygen is endowed with great chemical activity. 

 This activity we find exhibited in the first act of vegetar 



