22 HOW CROPS FEED. 
cur or may occur in the air in minute and variable quanti- 
ties, viz.: 
Water, as vapor...average Proper tion by WHEE 1)i00 
Carbonic acid gas sa a 8 [10-000 
Ammonia " “ te "|50- 000: 000 ? 
Ozone et fe ss ‘minute traces, 
Nitric acid “ oe 66 oe “6 “ 
Nitrous acid a “ oe “ iT3 it) 
Marsh gas cr “ nw ‘13 “ce “ 
In air of Carbonic oxide, a“ iT) a ac “ “ 
1 Sulphurous acid, fe Me ss “ ee “ 
sons. Sulphydrie acid xe iS ne a 
Miller gives for the air of England the following aver- 
age proportions by volume of the four most abundant in- 
gredients.—(Hlements of Chemistry, part IL. p. 30, 3d Ed.) 
ORY ON os iesiciesises cindaine meting asin aun te 20.61 
NGtrOS OM so icidisscie tie ctepe Vee aeedia. civie deeniete view TS 
Carbonic acid......... cece cece eee Seiswetee oie G04 
Water-vapor......ceeees Bsc Sisceiehstayendie Rrateaions 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 has, 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. 
§ 2 
RELATIONS OF OXYGEN GAS TO VEGETABLE NUTRITION. 
Absorption of Oxygen Essential to Growth.—The ele- 
ment Oxygen is endowed with great chemical activity. 
This activity we find exhibited in the first act of vegeta 
