Oil the Food of Flauts. 
511 
will bo found tlio namos of Ingonliaus, Spallanzani, Sonnobier, 
Theodore Do Saussure, and many others, was at onoc directed to 
tlie subject, by the researches of whom it was distinctly shown 
that this disengagement of oxygen was due to the decomposition 
of carbonic acid dissolved in the water by the green parts of 
plants, and further, that it only occurred under the influence of 
light. 
A modification of one of Sennebier s experiments made by the 
late Auguste de Candolle deserves particular notice. The fol- 
lowing is a translation of his own words: — 
" I placed on tlie same ]meumatic trough two inverted jars, tlie one 
A, as -well as the trough, filled with distilled water, in which floated a 
plant oi Menllia aquatica ; the other B, filled with caibonic acid gas. 
The water of the trough was covered by a thick layer of oil, to cut off 
communication for a time with tlie atmosphere ; the whole was exposed 
to the sun. Every day the gas in the jar B was seen to diminish, and 
the water to rise, while at the same time a nearly equal quantity of 
oxygen was collected in the jar A. During the tsvelve days of the 
experiment the mint preserved its healthy appearance, while a similar 
plant placed in a jar of distilled water exhibited signs of decomposition. 
Thus, in this experiment, carbonic acid gas was seen, as it were, to be 
distilled and decomposed by the i)lant, which was nourished by its means. 
The same experiment was repeated with oxygen in the place of carbonic 
acid, but no gas was disengaged in the jar containing the plant."* 
Dr. Gillyf placed a tuft of green grass in a jar containing a 
mixture of oxygen, nitrogen, and carbonic acid, and exposed the 
whole to the sun. After the lapse of four hours, the contents of 
the jar being examined, the greater part of the carbonic acid 
was found to be converted into oxygen. The analysis of the air 
gave: — 
Before Experiment. After Experiment. 
Cubic inches. Cubic inclies. 
Nitrogen 10 -.507 10-507 
Carbonic acid .... 5-7 0 37 
Oxygen 2-793 7-79 
19-0 18-667 
Thus, a growing plant in free air is seen to behave in precisely 
the same way as the water-mint of De Candolle. It is to be 
noticed that in the experiment related, a disappearance of oxygen 
to a small extent took place, a fact of some importance. 
The following experiments are by Theodore De Saussure :J — 
1. An artificial atmosphere was prepared in a large graduated 
jar secured over mercury covered with a film of water, consisting 
* De Candolle, Physiologie Vegetale, p. 1 — 121. 
f Lindley's Introduction, p. 312. 
■j; Recherches Chimiques sur la Vegetation, p. 40. 
VOL. IV. 2 L 
