Miscellaneous. 843 



compose carbonic acid and water, COS HO=CO, H, O^: the O" 

 being liberated, CO, H expresses the relation under which carbon is 

 united with the elements of water in cellulose, starch, sugar, &c., i. e. 

 in the important principles elaborated by the leaves, the composition 

 of which is represented by carbon and water. He goes on to prove 

 that a leaf which has been decomposing carbonic acid and water all 

 day long is capable of doing the same work the next day, if not 

 allowed to dry ; but the losing of a certain amount of water annihi- 

 lates this faculty, and irremediably destroys the life of the cells of a 

 leaf, vegetable life in this state being far less tenacious than that of 

 some of the lower animals (Tardigrades, Notipes, &c.), which bear 

 wonderful desiccation. 



The third instalment of the investigation is given in Nos. 16 and 

 17 of the same volume (Oct. 16 and 23, 1865). It appears that de- 

 tached leaves, kept in shade for many days, with the cut end of the 

 petiole in water to prevent desiccation, preserve the power of decom- 

 posing carbonic acid whenever brought into sunshine. But for this 

 they must be kept in an atmosphere containing a supply of oxygen ; 

 without this they soon die, as Boussingault thinks, from asphyxia. 

 This oxygen in darkness is slowly transformed into carbonic acid, 

 through an operation which is presumed to go on continually, whether 

 in light or darkness, and to answer to respiration. Of course a healthy 

 and active leaf decomposes far more carbonic acid in the light than 

 it forms in darkness. In eighteen experiments with oleander-leaves 

 exposed to the sun from 8 a.m. to 5 p.m. in an atmosphere rich in 

 carbonic acid, a square metre of foliage decomposed on the average 

 over a litre of carbonic acid per hour, while in darkness only y^ of 

 a litre of carbonic acid was produced per hour. In air which con- 

 tains oxygen and carbonic acid, leaves will go on indefinitely pro- 

 ducing oxygen in the presence of carbonic acid, and carbonic acid in 

 the presence of oxygen. But the latter, though relatively small in 

 amount, seems to be necessary to the preservation of their vitality. 

 In hydrogen, carburetted hydrogen, or nitrogen, as well as in pure 

 carbonic acid, they soon lose their decomposing power, and die from 

 the impossibility of respiration, i. e. are asphyxiated. 



Leaves confined in a limited portion of atmospheric or other air 

 over mercury lose the power of decomposing carbonic acid ; and the 

 experiments pretty clearly show that they lose it through the dele- 

 terious action of the vapour of mercury. It is thought remarkable 

 that the leaf does not under these circumstances at all lose the power 

 of transforming oxygen into carbonic acid ; but that is what we 

 should expect ; for the carbonic acid so evolved (whether its evolu- 

 tion be called respiration or not) must be a product of decomposition 

 of the leaf's contents or substance. 



We owe to Boussingault and his assistant Lewy the idea of deter- 

 mining the composition of the air contained in a fertile soil, and the 

 fact that this air in a strongly manured soil contains a very large 

 percentage of carbonic acid. Boussingault has now devised an ex- 

 periment by which the air contained in a branch of an oleander in 

 full vegetation was extracted. It proved to be, nitrogen 88'01 per 



