ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 45 
the plant exists. Corenwinder noticed that the evolution 
of carbonic acid in diffused light was best exhibited by 
very young plants, and mostly ceased as they grew older. 
Corenwinder has confirmed and extended these observa- 
tions in more recent investigations. (Ann. d. Sci. Nat., 
1864, I, 297.) 
He finds that buds and young leaves exhale carbonic 
acid (and absorb oxygen) by day, even in bright sunshine. 
He also finds that all leaves exhale carbonic acid not alone 
at night, but likewise by day, when placed in the diffused 
light of a room, illuminated from only one side. A plant, 
which i in full light yields no carbonic acid to a slow stream 
of air passing its folinge, immediately gives off the gas 
when carried into such an apartment, and vice versa. 
Amount of Carbonic Acid absorbed.—The quantity of 
carbonic acid absorbed by day in direct light is vastly 
greater than that exhaled during the night. According 
to Corenwinder’s experiments, 15 to 20 minutes of direct 
sunlight enable colza, the pea, the raspberry, the bean, 
and sunflower, to absorb as much carbonic acid as they 
exhale during a whole night. 
As to the xmount of carbonic acid whose carbon is re- 
tained, Corenwinder found that a single colza plant took 
up in one day of strong sunshine more than two quarts of 
the gas. 
Boussingault (Comptes Rend., Oct. 23d, 1865) found as 
the average of a number of experiments, that a square me- 
ter of oleander leaves decomposed in sunlight 1.108 liters 
of carbonic acid per hour. In the dark, the same surface 
of leaf exhaled but 0.07 liter of this gas, 
Composition of the Air within the Plant.—Full con- 
tirmation of the statements above made is furnished by 
tracing the changes which take place within the vegeta- 
ble tissues. Lawes, Gilbert, and Pugh, (Phd. Trans., 
1861, I, p. 486,) have examined the composition of the 
