IN THE VEGETABLE KINGDOM. 197 



as if it were deoxidised, exhibiting a decided process of reduction, 

 notwithstanding the absorption of oxygen. Liebig made observa- 

 tions of this nature on the formation of carbo-hydrates from 

 organic acids ; if, for instance, 6 equivalents of oxygen be added 

 to 6 equivalents of tartaric acid, and if 12 equivalents of carbonic 

 acid are developed therefrom, we obtain grape sugar, which is 

 relatively much poorer in oxygen (6C 4 H 2 O 5 + 6O 12 CO 2 = 

 C 12 H 12 O 12 ). Starch might be similarly formed from tannic acid 

 (C 18 H 6 O 10 + 8 O + 4 H O 6 C O 2 = C 12 H 10 O 10 ). If more complete 

 observations and experiments should enable us to prove that this 

 kind of deoxidising process has a more general application in the 

 vital economy of plants, many points might be explained which 

 still present considerable obscurity ; we might thus comprehend 

 why, notwithstanding the reversed interchange of gases which takes 

 place during the night, organic motion pursues its undisturbed 

 course after the restoration of the less oxidised matters; that is to 

 say, why the evolution of oxygen during the day is not exactly 

 balanced by the nocturnal absorption of that gas. We need then 

 no longer wonder that a plant may drag on a miserable existence 

 in an inclosed space, since it generates for itself through the day 

 the oxygen necessary for it during the night, and, conversely, 

 exhales the carbonic acid during the night, which is again to serve 

 for its nutrition through the day. This circulation of the oxygen 

 is only apparent, for the oxygen which has been separated from 

 its combination with carbon during the day, serves in the night to 

 extract a larger amount of oxygen, together with some of the 

 carbon of the organised matter. Thus we see by Erdmann's 

 admirable experiments on Tradescantia discolor, that a plant may 

 continue for years to vegetate in an unhealthy condition, although 

 without entirely dying, when placed in a hermetically closed 

 vessel. The death of some few leaves or stalks serves in these 

 cases merely to prolong the life of the plant, and to promote the 

 formation of new buds. The air within the inclosed space where 

 such plants had for a long time vegetated, would at length become 

 very rich in oxygen, if the above-mentioned parts, which die off, 

 did not contribute by their decomposition to supply the new 

 buds with carbon in the form of carbonic acid. If the nocturnal 

 interchange of gases in plants depends upon the process to which 

 we have here referred, the necessity of oxygen for the life of the 

 plant would be obvious, and we should have a simple explanation 

 of those experiments in which plants are found to vegetate in a 

 non-oxygenous air only so lon^ as the oxygen which is exhaled by 



