CH. ^TI.] THE FRUIT AND SEED. 215 



in their character. During their green and growing 

 state they are usually converting gummy matter into 

 an acid ; but during ripening they, as commonly, are 

 convertincr an acid into su^ar. 



To convert gum or mucilage into tartaric acid, as 

 in the early growth of the grape, oxygen in excess 

 should be absorbed, for their relative components 



stand thus : 



Grum. Tartaric Acid. 



Carbon . . . 42.23 . . 24.05 



Oxygen . . . 50.84 . . 69.32 



Hydrogen . . . 6.93 . . 6.63 



100.00 100.00 



They might therefore be expected to absorb more 

 oxygen than the leaves, and this is actually the case, 

 for though a vine branch will continue to vegetate 

 in a glass globe hermetically sealed, yet the grapes 

 upon it will not increase in size unless oxygen gas 

 be from time to time admitted. The same phe- 

 nomenon occm^s duiing the ripening of the grapes ; 

 oxygen has to be absorbed during the conversion of 

 the tartaric acid into sugar, but a larger volume of 

 carbonic acid has to be evolved, and this is coincident 

 with the result of well established experiments, 

 uniformly testifying that carbonic acid is given out 

 abundantly by ripening fruit. " Six equivalents of 

 tartaric acid," saysLiebig, " by absorbing six equiva- 



