36 ASSIMILATION Q\? HYDROGEN. 



annually to the atmosphere 2865 lbs., or 32,007 cubic feet of 

 free oxygen gas.* 



An acre of meadow, wood, or cultivated land, in general re- 

 places, therefore, in the atmosphere as much oxygen as is 

 exhausted by 10 cwts. of carbon, either in its ordinary combus- 

 tion in the air, or in the respiratory process of animals. 



It has been mentioned in a former part of the work that pure 

 woody fibre contains carbon and the component parts of water, 

 but that ordinary wood contains more hydrogen than corresponds 

 to this proportion. This excess is owing to the presence of the 

 green principle of the leaf, wax, oil, resin, and other bodies rich 

 in hydrogen. Water must be decomposed, in order to furnish 

 the excess of this element, and consequently one equivalent of 

 oxygen must be given back to the atmosphere for every equiva- 

 lent of hydrogen appropriated by a plant to the production of 

 those substances. The quantity of oxygen thus set at liberty 

 cannot be insignificant, for the atmosphere must receive above 

 100 cubic feet of oxygen for every pound of hydrogen 

 assimilated. 



It has already been stated, that a plant, in the formation of 

 woody fibre, must always yield to the atmosphere the same pro- 

 portional quantity of oxygen ; and that the volume of this gas 

 set free would be the same whether it were due to the decompo- 

 sition of carbonic acid or of water. It was considered most pro- 

 bable that the latter was the case. 



From their generating caoutchouc, wax, fats, and volatile oils 

 containing hydrogen in large quantity, and little oxygen, we may 

 be certain that plants possess the property of decomposing 

 water, because from no other body could the unazotized sub- 

 stances obtain their hydrogen. It has also been proved by the 

 observations of Humboldt on the fungi, that water may be decom- 

 posed without the assimilation of hydrogen. Water is a remark- 

 able combination of two elements, which have the power to sepa- 

 rate themselves from one another, in innumerable processes, in 

 a manner imperceptible to our senses ; while carbonic acid, 



* The specific weight of oxygen is expressed by the number T1026 ; 

 hence, 1 cubic metre of oxygen weighs 3 - 157 lbs., and 2865 lbs. of oxygen 

 correspond to 90S cubic metres, or 32,007 cubic feet. 



