ATMOSPHKIMC AIll AS THU 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. N'at.^ 

 1864, I, 297.) 



He finds that buds and young leaves exhale carbonic 

 acid (and absorb oxygen) l)y 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 in full light yields no carbonic acid to a slow stream 

 of air passing its foli:ige, immediately gives off the gas 

 when carried into such an apartment, and vice versa. 



Amount of Tarbonic Acid absorbed. — The quantity of 

 oarbonic acid absorbed by day in direct light is vastly 

 greater than that exhaled during the night. According 

 to Coren winder'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 amount 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 ill sunlight 1.108 liters 

 of carbonic acid per hour. In the dark, the same surface 

 of leaf exhaled but 0.07 liter of this g.is. 



Composition of tlie Air within the Plant. — Full con 

 tirmation of the statements above made is furnished by 

 tracing tlie changes which take place within the vegeta- 

 ble tissues. Lawes, Gilbert, and Pugh, {Phil Trans.^ 

 1861, II, p, 486,) have examined the composition of the 



