4 
WeVIolON F. 
THE ATMOSPHERE AS RELATED TO 
VEGETATION. 
CHAPTER. y- 
ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 
§ 1. 
CHEMICAL COMPOSITION OF THE ATMOSPHERE. 
A multitude of observations has demonstrated that 
from ninety-five to ninety-nine per cent of the entire mass 
(weight) of agricultural plants is derived directly or indi- 
rectly from the atmosphere. 
The general composition of the Atmosphere is familiar 
to all. It is chiefly made up of the two elementary ga-es, 
Oxygen and Nitrogen, which have been described in “ How 
Crops Grow,” pp. 33-39.* These two bodies are present 
in the atmosphere in very nearly, though not altogether, 
invariable proportions. Disregarding its other ingredients, 
the atmosphere contains in 100 parts | 
By weight. By volume. 
Ceyens cher: Soe pe, ln PAN ee 20.95 
INSGPD EN i ae ays neds vj gs = ef OR hare ye 79.05 
100.00 100.00 
Besides the above elements, several other substances oc- 
* In our frequent references to this book we shall employ the abbreviation 
H.C. G. &. “f IFGy 
21 
