THE CHEMISTRY OF FRUIT-RIPENING. 465 



The green plums contain tannin, which commenced to diminish as 

 soon as the fruit began to emit carbonic acid in the daylight, wholly 

 disappearing by June 20th, the date at which the malic acid began to 

 diminish. It is well known to every one that many green fruits are 

 very astringent, and that their tannin decreases and sometimes dis- 

 appears during ripening. Also, it is a familiar fact in the chemistry 

 of tannin that it readily undergoes changes producing sugar. This, 

 then, is the source of a portion of the sugar of many fruits. The 

 formation of sugar from tannin will be discussed under the head of 

 the glucosides of fruits. 



Several chemists have reported the presence of sugar-producing 

 substances peculiar to fruits. Buignet describes a fruit constituent, 

 astringent like tannin, and combining with iodine like starch, and 

 serving as the source of sugar. 



The proportion of cane-sugar, in most fruits, is generally believed 

 to diminish by transformation into glucose, as fruits become fully 

 ripe or overripe. But Berthelot and Buignet ( Comptes Bendus, li., 

 1094) found that, in oranges, the proportion of cane-sugar increased 

 during ripening, the quantity of glucose remaining unchanged. 



The increase of weight of fruits, during ripening, is no doubt 

 largely owing to deposition of sugar. Berard found that 100 parts 

 of unripe summer peaches yielded 179 parts of ripe fruit, and 100 

 parts of unripe apricots increased in ripening to 200 parts. 



The maturity of fruit is the period of its maximum quantity of 

 sugar. Sooner or later, the quantity of sugar begins to diminish, and 

 then the fruit is overripe. It is safe to say that the sugar often 

 begins to decompose during the life of the fruit; that is to say, fruit 

 becomes overripe during its life. It would be difficult, however, to 

 fix on the termination of the life of fruit. We certainly cannot say 

 that life ceases when the circulation with the plant is cut off; and we 

 cannot say that life continues in the sarcocarp until it is wholly dis- 

 integrated. Now it is within the limits of our subject to inquire by 

 what changes the sugar begins to disappear. 



In general terms, sugar sutlers oxidation in ripe fruits, small por- 

 tions being oxidized away even during the production of larger por- 

 tions, and before perfect maturity. We do not know what fruit con- 

 stituents, if any, result in this oxidation. The final products of oxi- 

 dation, carbonic acid and water, are exhaled during ripening, and 

 with greater rapidity after maturity has been passed. 



It seems to be established that sugar in fruits is liable to traces of 



VOL. XII. 30 



