L 205 J 



f 



probably have greater power to absorb carbonic acid 

 from the atmosphere, when the water is saturated with 

 carbonic acid gas, some of this substance, even in the 

 sunshine, may be given off by the leaves; but a part of" 

 it likewise will be always decomposed, which has been 

 proved by the experiments of M. Sennebier. 



When the fluid taken up by the roots of plants 

 contains much carbonaceous matter, it is probable 

 that plants may give off carbonic acid from their leaves, 

 even in the sunshine. In short, the function of the 

 leaf must vary according to the composition of the sap 

 passing through it. When sugar is to be produced, 

 as in early spring at the time of the development of 

 buds and flowers, it is probable that less oxygene will 

 be given off, than at the time of the ripening of the 

 seed, when starch, or gums, or soils, aite formed; and 

 the process of ripening the seed usually takes place 

 when the agency of the solar light is most intense. 

 When the acid juices of fruits become saccharine in the 

 natural process of vegetation, more oxygene, there 

 is every reason to believe, must be given off, or new- 

 ly combined, than at other times; for, as it was shewn 

 in the third Lecture, all the vegetable acids contain 

 more oxygene than sugar. It appears probable, that 

 in some cases, in which oily and resinous bodies are 

 formed in vegetation, water may be decomposed: its 

 oxygene set free, and its hydrogene absorbed. 



I have already mentioned, that some plants pro- 

 duce oxygene in pure water; Dr. Ingenhousz foinid 

 this to be the case with species of the confervas; I 

 have tried the leaves of many plants, particularly those 





