THE VOLATILE PART OF PLANTS. 77 



ture of the three sugars with some gum. The mannas of 

 Syria and Kurdistan are of similar composition. 



The older observers assumed the presence of glucose in 

 the bread grains. Thus Vauquelin found, or thought he 

 found, 8.5 1 of this sugar in Odessa wheat. More recent- 

 ly, Peligot, Mitscherlich, and Stein have denied the pres- 

 ence of any sugar in these grains. In his work on the 

 Cereals and Bread, (Die Getreidearten und das JZrod, 

 I860,) p. 163, Yon Bibra has reinvestigated this question, 

 and found in fresh ground wheat, etc., a sugar having 

 some of the characters of saccharose, and others of glucose 

 and levulose. It is, therefore, a mixture. 



Von Bibra found in the flour of various grains tlie following quan- 

 tities of su^ar. 



PROPORTIONS OF SUGAR IN AIR-DRY FLOUR, BRAN, AND MEAL. 



Per cent. 



Wheat flour 2.33 



Spelt flour 1.41 



Wheat bran , 4.30 



Spelt bran 2.70 



Rye flour 3.46 



Rye bran 1.86 



Barley meal 3.04 



Barley bran 1.90 



Oat meal 2.19 



Rice flour 0.39 



Millet flour 1.30 



Maize meal 3.71 



Buckwheat meal 0.91 



Glucosides. There occur in the vegetable kingdom a 

 large number of bodies, usually bitter in taste, which con- 

 tain " glucose, or a similar sugar, chemically combined 

 with other substances, or yield it on decomposition. 

 Tannin, the bitter principle of oak and hemlock bark ; 

 saHcin, from willow bark ;. phloridzin, from the bark of 

 the apple-tree root, and principles contained in jalap, 

 scammony, the horse chestnut, and almond, are of this 

 kind. The sugar may be obtained from these so-called 

 glucosidcs by heating with dilute acids. 



