238 
cy of carbonic matter, deeming it probable that .the 
quantity of oxygen and hydrogen in plants cannot be 
increased beyond certain limits, unless the carbon be 
supplied in proportion* To verify this idea, he re- 
fers to the experiments made on plants which grew 
in atmospheres of common air containing carbonic 
acid (310.), and in which that gas was decomposed j 
and oxygen gas expelled. He considers the carbon, 
which was previously united with this oxygen, to have 
been assimilated by the plant, and thereby to have 
augmented its vegetable substance, Thus the 21.75 
cubic inches of carbonic acid, decomposed by the se- 
ven plants of I'inca minor 9 afforded to the plants 4.2 
grains of carbon. These plants weighed, in their 
green state, before the experiment, 168* grains, and 
contained 5 1 grains of dry vegetable matter ; but, 
when reduced to dryness after the experiment, their 
weight amounted to 61 grains; so that, after thus 
decomposing the carbonic acid, their vegetable sub- 
stance, it is said, was increased by ten grains. But 
of these ten grains, 4.2 only can be attributed to the 
carbon of the acid, and therefore the remaining weight, 
equal to 5.8 grains, must, says M. de Saussure, be 
ascribed to the fixation or solidification of water. 
Plants of mcntha aquatica, in the same manner, aug- 
mented their dry vegetable substance by six grains, 
of which one half is ascribed to the assimilation of 
carbon, and the other half to the fixation of water *. 
523. In opposition to this view of vegetable nutri- 
tion, we may observe, that etiolated plants, which 
* Rechcrches Cliini. p. 225. 
