THE CHEMISTRY OF FRUIT RIPENING. 151 



1. Sugars (starches). 



2. Pectous sub:stances and gurus. 



3. Acids, tannin and otlier glucosides. 



4. Ethers. 



5. 7\.lkaloids. 



The analyses of fruits hitlierto reported have mostly been made by European 

 chemists. The fullest reports of ripe fruits, upon Avhich I am in good part 

 dependent, were made by Fresenius, from analyses under his direction, nearly 

 twenty years ago, and represent the fruits of tlic llhine district, obtained at 

 Wiesbaden. 



1. Sugars. The prevailing sugar in fruits is glucose (dextrose), often termed 

 grape sugar. It is the same compound that is largely manufactured from 

 starcli, and called starch sugar. It is mucli less sweet than cane-sugar and less 

 abundantly soluble in water, having an oily or ''mealy" taste. As made from 

 starch, it is now much used in certain candies. AVhcn in tlie nncrystallizable 

 form, glucose (Icevulose) is tlie same as "fruit-sugar," tlie unci'ystallizable pro- 

 duct obtained to some extent in manufacturing cane-sugar, and whicli forms a 

 part of the syrups of tlie market. Many of the fruits contain cctnc-sugar 

 (which is the same as beet-sugar and maple-sugar), and certain rare varieties 

 of sugar are found in some fruits. 



Buignet decided that the apple, peach, plum, raspberry, orange, and pine- 

 apple contain cane-sugar, witli glucose (mostly as Uevulose). The sugar of the 

 grape, cherry, gooseberry, and fig, consists wholly of glucose. 



The average proportion of sugars in ripe fruits is given, by Fresenius, as 

 follows (the smallest per centages being placed first) : 



Peaches, 1.6 per cent, (not varying very widely). 



Apricots, 1.8 per cent (from 1.1 to 2.7). 



Plums, round red, 3.1 per cent, (from 2.0 to 3.5). 



Greengages, 3.1 per cent. 



Kaspberries, 4.0 per cent, (from 3.0 to 5.0). 



Blackberries, 4.4 jier cent. 



Strawberries, 5.7 per cent, (from 3.3 to 7.6). 



Currants, 6.1 per cent (from 4.8 to (j.(j). 



Gooseberries, 7.1 per cent, (from 6.0 to 8.3). 



Pears, red, 7.4 per cent. 



Apples, 8.4 per cent, (from 5.9 to 10.4). 



Cherries, 9.8 per cent, (from 8.5 to 13.1). 



[Summer peaches 11. G per cent. Berard's analysis.] 



Grapes, 14.9 per cent, (from 13 to 19). 



It is seen from this list that tlie sweetness of fruit has but slight correspon- 

 dence witli its proportion of sugar. Currants were found to have more sugar 

 than raspberries, bhickberrics or strawberries, and over three times as much as 

 the peaclies examined by Fresenius. All analysts agree in the predominence 

 of grapes for tlieir quantity of sugar. The sweetness of fruit is probably 

 favored less by large proportions of sugar, than by three other conditions, 

 luunely : ( 1), small proportions of acids, (2) large proportions of pectous sub- 

 stances, (3) presence of cajie-sugar instead of grape sugar. 



The sicgar of fruits is chief g formed or deposited in them during their ripen- 

 ing. Berard found that the pulp of cherries, unripe, contained only 1.1 per 

 cent, of sugar; ripe, 18.1 per cent.; gooseberries, unripe, 0.5 per cent.; ripe, 

 Q.% per cent. In 1862, Hilger determined the sugar of grcqjcs^ at ten periods 



