AERATION OF THE SAP. 27 



to show that the violet, or most refrangible of the 

 solar rays, have the greatest power in determining 

 this decomposition of carbonic acid ; but the experi- 

 ments are of so delicate a nature, that this result 

 requires to be confirmed by a more rigid investi- 

 gation, before it can be admitted as satisfactorily 

 established. 



That the carbon resulting from this decompo- 

 sition of carbonic acid is retained by the plant, 

 has been amj^ly proved by the experiments of 

 M. Theodore de Saussure, who found that this pro- 

 cess is attended with a sensible increase in the 

 quantity of carbon which the plant had previously 

 contained. 



It is in the chlorophyUite, or green substance of 

 the leaves alone that this process is conducted ; 

 a process, which, from the strong analogy tliat it 

 bears to a similar function in animals, may be con- 

 sidered as the /7?6y;z>«//o/i of vegetables. The effect 

 appears to be proportionate to the number of 

 stomata which the plant contains. It is a process 

 which takes place only in the living plant; for if a 

 leaf be bruised so as to destroy its organization, and 

 consequently its vitality, its substance is no longer 

 capable either of decomposing carbonic acid gas 

 under the influence of solar light, or of absorbing 

 oxygen in the dark. Neither the roots, nor the 

 flowers, nor any other parts of the plant, which 

 have not this green substance at their surface, are 

 capable of decomposing carbonic acid gas: they 

 produce, indeed, an effect which is in some respects 

 the opposite of this ; for they have a tendency to 

 absorb oxygen, and to convert it into carbonic 

 acid, by uniting it with the carbon they themselves 



