EASILY CONVERTED INTO SUGAR. 71 



simply, as is proved by analysis, on the addition of the 

 elements of water. (12) All the carbon of the starch 

 is found in the sugar ; none of its elements have been 

 separated, and, except the elements of water, no 

 foreign element has been added to it in this trans- 

 formation. 



In many, especially in pulpy fruits, which when 

 unripe are sour and rough to the taste, but when 

 ripe are sweet, as, for example, in apples and pears, 

 the sugar is produced from the starch which the un- 

 ripe fruit contains. 



If we rub unripe apples or pears on a grater to a 

 pulp, and wash this with cold water on a fine sieve, 

 the turbid liquid which passes through deposits a 

 very fine flour of starch, of which not even a trace 

 can be detected in the ripe fruit. Many varieties 

 become sweet while yet on the tree ; these are the 

 summer or early apples and pears. Others, again, 

 become sweet only after having been kept for a cer- 

 tain period after gathering. The after-ripening, as 

 this change is called, is a purely chemical process, 

 entirely independent of the vitality of the plant. 

 When vegetation ceases, the fruit is capable of re- 

 producing the species, that is, the kernel, stone, or 

 true seed is fully ripe, but the fleshy covering from 

 this period is subjected to the action of the atmo- 

 sphere. Like all substances in a state of erema- 

 causis, or decay, it absorbs oxygen, and gives off a 

 certain quantity of carbonic acid gas. 



In the same way as the starch in putrefying paste, 



