I 



SUGARS 45 



are so called since they respectively split up, under certain cir- 

 cumstances, into two or many molecules of monosaccharides. 

 Among the monosaccharides found in plants, the commonest 

 are dextrose or glucose (popularly known as grape-sugar) and 

 fructose or levulose (fruit-sugar), whilst of the disaccharides 

 sucrose or saccharose (cane-sugar) and maltose (malt-sugar) 

 deserve mention. Owing to their simple molecules they produce 

 a relatively high osmotic pressure, although for solutions of 

 equal strength this is greater in the case of the monosaccharides 



In 



FIG. 21. Sphere-crystals of inulin (In.) in the cells of the tuberous root 



of a Dahlia. 



than in that of the disaccharides. For this reason no doubt 

 grape-sugar and cane-sugar, the two which function as food- 

 reserves, are only found in very minute quantities in seeds 

 (except for the cane-sugar in the Sweet Corn, a variety of Maize). 

 On the other hand, grape-sugar is one of the principal carbo- 

 hydrate-reserves in the bulb of the Onion, whilst cane-sugar 

 occurs in the Sugar Beet (Beta), in the pith of the stem of the 

 Sugar Cane (Saccharum officinarum), and in the Sugar Maple 

 (Acer sacchatinum) (see p. 124). The sugar is extracted from 

 the sliced Beet with the aid of warm water, whilst in the case 



