THE CIIEMLSTllY OF FRUIT RIPENING. 153 



The green plums contained tannin, which commenced to diminish as soon 

 as the fruit began to emit carbonic acid in the daylight, ^vholly disapjicaring by 

 June ^Oth, tlie date at which the malic acid began to diminisli. It is wefl 

 known to every one that numy green fruits are very astringent, and that their 

 tannin decreases and sometimes disappears during ripening. Also, it is a famil- 

 iar fact in tlio chemistry of tannin that it readily undergoes changes producing 

 sugar, Tliis, then, is the source of a portion of the sugar of nniny fruits, Tlie 

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

 sides of fruits. 



Several chemists have reported the presence of sugar-producing substances 

 peculiar to fruits, Buignetdescriljcs a fruit constituent, astringent like tannin, 

 and combining witli iodine like starch, and serving as the source of sugar. 



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

 ish by transformation into glucose, as fruits become fully ripe or over-ripe. 

 But Berthelot and Buignct (Compt. rend., 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 1T9 jDarts of ripe fruit" and 100 parts of unripe apricots increased in 

 ripening to 200 joarts. 



The maturity of fruit is tlie period of its maximum quantity of sugar. 

 Sooner or later, the quantity of sugar Icgins to diininisJi, and then the fruit is 

 over-ripe. It is safe to say that the sugar often begins to decompose during 

 the life of the fruit ; that is to say, fruit becomes over-ripe 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 ig what 

 changes the sugar legins to disappear. 



In general terms, sugar suffers oxidation in ripe fruits, small portions being- 

 oxidized aw^ay even during the production of larger portions and before perfect 

 maturity, A\^c do not know what fruit constituents, if any, result in this oxi- 

 dation. Tlie /i;ia/ products of oxidation, 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 the alco- 

 \\o\\G fermentation, even before maturity is passed. II. Gutzeit (Zeitschr. Oest. 

 Ap. Ver., 1875, p, 337; Pro, Am, Phar, Asso., 187G, p. 287) reports finding 

 alcohol, or other simple compound of ethyl, in the fruits of a number of 

 plants. Some of the fruits were not quite ripe, and none were over-ripe. De 

 Luca (Compt. rend., Ixxxiii, 512; Jour. Chem. Soc, 1876, II., G49) reports 

 obtaining products of the alcoholic and acetic fermentations, from the fresh 

 fruits, leaves and flowers of several plants. In all these cases, the quantities 

 of alcohol obtained were very minute. The investigator first above named 

 found methyl alcohol, in some cases, with the ethyl alcohol, Pasteur states 

 that the germs which excite alcoholic fermentation are very abundant on the 

 bunches of ripe grapes, where very rare in the atmosphere. Also, that the fer- 

 mentive germs are found on ripe strawberries, cherries, and currants, but not on 

 the same fruits irnripe. The formation of methyl alcohol, above referred to, 

 is closely allied to the formation of methyl salicylate or wintergreen oil. A 

 number of the essential or volatile oils, witli which plants and fruits are per- 



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