IN THE VEGETABLE KINGDOM. 181 



the oxygen that is absorbed are entirely dependent on the chemical 

 constituents of the leaves. Thus, for instance, leaves which are 

 proportionally rich in substances poor in oxygen, as for example, 

 resinous ethereal oils, which even in their isolated state readily 

 become more highly oxidised when exposed to the action of the 

 air, are also found to absorb a relatively larger quantity of oxygen 

 in the dark. 



A complete process of acidification during the night, as the 

 effect of oxidation, is occasionally met with in the leaves of certain 

 plants, as, for instance, the Cacalia fico'ides, Cotyledon calycma, and 

 others, which, after being tasteless at noon, have a bitter taste in 

 the evening, but are sharply acid in the morning. 



Pelouze has shown that tannic acid is converted into gallic and 

 carbonic acids by the absorption of 8 atoms of oxygen (C 18 H 8 O 12 

 + 8O = 4CO 2 + 2C 7 H 3 O 5 . HO). We cannot wonder at the 

 fact observed by Saussure, that the leaves of the oak, which are so 

 rich in tannic acid, should absorb 14 times their volume of oxygen 

 during 24 hours when in the dark, whilst the tasteless and scent- 

 less leaves of the Agave americana can scarcely absorb 3-10ths of 

 their volume in the same time. The leaves of the white poplar, 

 which contain a very resinous or oxidisable oil, absorb as much as 

 21 times their volume of oxygen in 24 hours. 



Without entering more fully into the question of the respective 

 results of these two reciprocally suspended processes of the 

 vegetable kingdom, we would simply observe that, notwithstanding 

 the grounds on which Liebig supports his view of the purely 

 chemical nature of the absorption of oxygen, this process and the 

 separation of carbonic acid, appear, from numerous phyto- 

 physiological experiments, to stand in a more direct relation to the 

 whole life of the plant ; and that, in the vegetable kingdom, pro- 

 cesses of oxidation also occur in addition to the preponderating 

 processes of deoxidation, in the same manner as we find that, in 

 the animal organism, where life is so thoroughly characterised 

 by continuous oxidation, processes of deoxidation may yet also 

 occur, as, for instance, in the formation of fat from sugar and 

 amylaceous substances. This is, however, so decidedly a purely 

 phy to-physiological question, that it scarcely falls within the scope 

 of our inquiries. According to our view, Liebig has given the 

 most striking and ingenious proofs that the vegetable kingdom 

 derives its large supply of carbon from the atmosphere alone, and 

 that plants alone possess the faculty of generating organic matter 

 from inorganic substances. 



