58 PLANT COMPOUNDS 



in sweet fruits, stalks of corn and sugar cane, in seeds, roots, 

 bulbs, and the sap of maple, birch, and other trees. Sugar 

 cane and sugar beets are the principal sources of sucrose, 

 the former containing about 20 per cent., the latter, 15 

 per cent. Fig. 12 illustrates the harvesting of a crop of 

 sugar cane, and Fig. 41 a growing crop of sugar beets. 

 From the physiological point of view, sucrose is a storage 

 form of carbohydrates, particularly in roots and tubers such 

 as beets and sweet potatoes, it being formed in all proba- 

 bility by a condensation of dextrose and the elimination of 

 water. 



Sucrose is a colorless solid, crystallizing in large, clear 

 crystals (Fig. 13). As it is usually purchased, it consists 

 of very small crystals, the mass of which appears white due 



Fig. 13. — Crystal of sucrose. Natural size. Drawing by C. A. Smith. 



to reflected light. It is easily soluble in water, slightly 

 soluble in hot absolute alcohol, more easily soluble in dilute 

 alcohol, insoluble in ether and in cold absolute alcohol. It 

 is dextrorotatory, the specific rotation being +66.5°. Its 

 sweetness is too well known to need description. 



Sucrose does not reduce Fehling's solution, that is, it is 

 not easily oxidized. It melts at about 160° C. From 170° 

 up to 190° C. it decomposes, by losing water, to a mixture 

 of unknown condensation products, the mass turning brown 

 in color and having a peculiar, agreeable flavor. Caramel 

 is the name given to the material. Caramel is soluble in 

 water, reduces Fehling's solution, and is used to a large 

 extent as flavoring for candy and ice-cream. 



Under the action of an enzyme called invertase, sucrose 



