46 HOW CROPS FEED. 
air contained in plants, as well when the latter are remov- 
ed from, as when they are subjected to, the action of light. 
To collect the gas from the plauts, the latter were placed 
in a glass vessel filled with water, from which all air had 
been expelled by long boiling and subsequent cooling in 
full and tightly closed bottles. The vessel was then con- 
nected with a simple apparatus in which a vacuum was 
produced by the fall of mercury, down a tube of 30 inches 
height. The air contained within the cells of the plant 
was thus drawn over into the vacuum and collected for 
examination. We give some of the results of the 6th 
series of their examinations. “The Table shows the 
Amount and Composition of the Gas evolved into a Tor- 
ricellian vacuum by duplicate portions of oat-plant, both 
kept in the dark for some time, and then one exposed to 
sunlight for about twenty minutes, when both were sub- 
mitted to exhaustion.” 
Per cent. 
Date Conditions | Cubic centimeters 
1858. during of | Nitrogen., Oxygen.| Carbonic Acid. 
* | Eehaustion. Gas collected. 
{In dark. 24.0 Re 77.08 3. 19.17 
daly 31.17 9p sunlight. 34.5 68.69 24.93 6.38 
Aug. 9,| J im dark. 10.6 68.28 10.21 21 51 
oe ada I sunlight. 39.2 67.86 25.95 6.89 
Aue. 9, J 1 dark, 30.7 76.87 8.14 14.99 
s° “|| In sunlight. 26.5 69.43 20.17 3.40 
These analyses show plainly what it is that happens in 
the cells of the plant. The atmospheric air freely pene- 
trates the vegetable tissues, (H. C. G., p. 288.) In dark- 
ness, the oxygen that is thus contained within the plant 
takes carbon from the vegetable matter and forms with it 
carbonic acid. This process goes on with comparative 
rapidity, and the proportion of oxygen may be diminish- 
ed from 21, the normal percentage, to 4, or even, as in 
some other experiments, to less than 1 per cent of the 
volume of the air. Upon bringing the vegetable ‘tissue 
into sunlight, the carbonic acid previously formed within 
the cells undergoes decomposition. with separation of its 
