336 CHEMISTRY. 



have beautiful examples of the change of starch and even 

 of wood into sugar in different plants. Fruits that become 

 sweet as they ripen have their starch converted into sug- 

 ar. This can be proved by the application of the iodine 

 test ( 452). If tincture of iodine be applied to the fruit 

 when green, you will have the characteristic blue color of 

 iodide of starch; but if it be applied when the fruit is fully 

 ripe, no such color appears. When sugar -forms so abun- 

 dantly in the sugar-maple in the early spring it comes 

 partly from the conversion of the starch in the tree, and 

 probably some of its wood, into sugar. 



464. Wood and Starch made from Sugar. Wonderful as 

 are the changes effected by art, as described in 461, still 

 more wonderful are those which are effected by nature. 

 The chemist can only produce one of the sugars from wood 

 and starch, and that of a poorer kind, while nature can not 

 only produce all kinds, but can change them back as occa- 

 sion requires into starch and wood. For example, the sap 

 of the maple loses its abundant sweetness as the leaves put 

 forth, the sugar in it being converted into wood in the an- 

 nual growth of the tree. So, also, in the case of the sugar- 

 beet, if left too long in the ground much of the sugar 

 changes into wood, making the beet tough and fibrous. If 

 grass be not cut soon enough, the hay is deficient in sweet- 

 ness, and is too coarse and strong, because much of the 

 sugar in its juice has been turned into wood. In cutting 

 the sugar-cane the tops are rejected, because they have 

 so little sugar in them. The reason of this is, that as 

 the plant grows upward the sugar is used up in making 

 the woody structure, but as soon as any of the struct- 

 ure is completed the cells in it are filled with the sugary 

 juice. The lower part, therefore, being complete, is fully 

 charged, while the upper part, which is growing, is not. 



465. Honey. The bee gathers sugar in the form of honey 



