464 THE POPULAR SCIENCE MONTHLY. 



1. 

 2. 

 3. 

 4. 

 5. 



(5. 

 7. 

 8. 

 9. 

 10. 



Austrian. 



June 27th | 1.37 per cent. 



August 10th 1.33 " " 



August 22(1 : 2.18 " " 



August 28th j 4.25 " " 



September 1st 2.53 " " 



September 12th j 4.49 " " 



September 17th ' 5.33 " " 



September 23d , 7.71 " " 



October 10th | 9.90 " " 



November 10th I 9.90 " " 



Riesling. 



1.01 per cent. 



1.23 " " 



1.81 " " 



2.39 " " 



2.58 " " 



2.89 " " 



3.87 " " 



7.70 " " 



8.64 " " 



8.21 " " 



Whether the sugar of fruits is formed within them, or introduced 

 through the stem, and, if formed in the fruits, from what substance 

 formed, are questions which have been investigated, but not wholly 

 settled. It has been pretty generally held that starch in the unripe 

 fruits is converted into sugar in the ripe fruits; the fruit acids induc- 

 ing the change, as we know they have power to do. But starch is 

 not found in the unripe stage of all fruits, and, in the cases where 

 found, its quantity is sometimes too small to serve as the source of all 

 the sugar of the ripened fruit. In the investigation of Hilger, above 

 quoted, the immature fruit was at no time found by microscopic ex- 

 amination to contain starch. It appeared in the fruit-stalks in June ; 

 after August it almost wholly disappeared from the fruit-stalks, and 

 was found only in the wood of the vines. Payen {Comptes Hendus, 

 liii, 313) reported that he had demonstrated the presence of starch in 

 unripe fruits and its conversion to sugar during ripening ; but did not 

 ascertain how much of the sugar of fruits is formed in this way. 



It has been advanced that sugar is formed from malic and other 

 acids, during ripening, either in the fruit or in the parts of the plant 

 supplying juices to the fruit. Six molecules of malic acid and six 

 molecules of tartaric acid, with nine molecules (eighteen atoms) of 

 oxygen, would furnish the atoms for formation of four molecules of 

 glucose, twelve molecules of water, and twenty-four molecules of car- 

 bonic anhydride. Mercadante (Gazetta Chimica Italiana, cxxv. ; Jour- 

 nal of the Chemical Society, xxviii. [1875], 904) made a series of de- 

 terminations of the malic acid and sugar in plums, commencing May 

 20th. The quantities of both acid and sugar increased in" the fruit so 

 long as it was green and emitting oxygen in the daylight; the 

 branches which bore the fruit containing acid and pectous substances 

 but no sugar. During the same time, the pectous and gummy sub- 

 stances in the green fruit had decreased from six per cent, of the pulp 

 to three per cent, of the pulp. The investigator believed the sugar 

 of the green fruit to have been chiefly formed, in the fruit, from the 

 pectous and gummy substances, under contact of the acids. As soon 

 as the fruit, losing green color, began to emit carbonic acid in the 

 daylight, the acid in it began steadily to decrease as the sugar in- 

 creased. The increase of sugar at expense of the acid in the pulp of 

 plums is shown as follows : 



