82 ASSIMILATION OF HYDROGEN 



unites directly with water, or the hydrogen of water 

 combines with the oxygen of the carbonic acid. In 

 the former of these cases, the two equivalents of ox- 

 ygen in the carbonic acid must be liberated; in the 

 latter, two atoms of water must be decomposed, the 

 hydrogen of which unites with the oxygen of the 

 carbonic acid, whilst the oxygen of the water, thus 

 set free, is disengaged in the state of a gas. It 

 was considered most probable that the latter was 

 the case. 



From their generating caoutchouc, wax, fats, and 

 volatile oils containing hydrogen in large quantity, 

 and no oxygen, we may be certain that plants pos- 

 sess the property of decomposing water, because 

 from no other body could they obtain the hydrogen 

 of those matters. It has also been proved by the 

 observations of Humboldt on the fungi, that water 

 may be decomposed without the assimilation of hy- 

 drogen. Water is a remarkable combination of 

 two elements, which have the power to separate 

 themselves from one another, in innumerable pro- 

 cesses, in a manner imperceptible to our senses ; while 

 carbonic acid, on the contrary, is only decomposable 

 by violent chemical action. 



Most vegetable structures contain hydrogen in 

 the form of water, which can be separated as such, 

 and replaced by other bodies ; but the hydrogen 

 which is essential to their constitution cannot pos- 

 sibly exist in the state of water. 



All the hydrogen necessary for the formation of 

 an organic compound is supplied to a plant by the 

 decomposition of water. The process of assimila- 

 tion, in its most simple form, consists in the extrac- 

 tion of hydrogen from water, and carbon from car- 

 bonic acid, in consequence of which, either all the 

 oxygen of the water and carbonic acid is separated, 

 as in the formation of caoutchouc, the volatile oils 

 which contain no oxygen, and other similar sub- 

 stances, or only a part of it is exhaled. 



The known composition of the organic compounds 



