254 ACTION OF FRUIT ON ATMOSPHERE. [BOOK n. 



same, they consume more oxygen in darkness when distant 

 from ripeness, than when they are approaching that state. If 

 exposed to the sun, they disengage altogether or in part the 

 oxygen which they inhaled during the night, and preserve no 

 trace of this acid in their own atmosphere. If many fruits are 

 detached from the plant, they thus add oxygen to air which 

 contains no carbonic acid. When their vegetation is very 

 feeble, or extremely languid, they vitiate the air under all 

 circumstances, but less in the sun than in the shade. Green 

 fruits detached from a plant, and exposed successively to the 

 action of the sun and of darkness, change it but little or not 

 at all either in purity or in volume. The trifling variations 

 that may be remarked in this respect depend either upon the 

 greater or less faculty which they have of elaborating carbonic 

 acid, or on their composition, which is modified according to 

 the degree of their ripeness. Thus Grapes, in a state of ver- 

 juice, appear to assimilate in small quantity the oxygen of the 

 carbonic acid which they form in the air where they vegetate 

 both day and night ; while, on the contrary, Grapes nearly 

 ripe give back almost entirely, during the day, to their own 

 atmosphere, the oxygen of the carbonic acid they have formed 

 in darkness. If there is no deception in this circumstance, 

 which, although feeble, appears to have been constant, it 

 marks the passage from the acid to the sweet state, by indi- 

 cating that the acidity of verjuice depends upon the fixing of 

 the oxygen of the air, and that this acidity disappears when 

 the fruit no longer seeks for carbon in the air or in carbonic 

 acid. Green fruits decompose, either entirely or in part, 

 not only the carbonic acid they have produced during the 

 night, but, in addition, such quantity as may be artificially 

 added to their atmosphere. When this last experiment 

 is tried with fruits which are not watery, and which, 

 like Apples and Grapes, elaborate carbonic acid slowly, 

 one sees that they absorb in the sun a much larger pro- 

 portion of gas than the same volume of water in a similar 

 mixture ; afterwards they disengage the oxygen of the car- 

 bonic acid absorbed, and thus appear to elaborate it in their 

 interior. 



"They appropriate to themselves during their vegetation 



