SUGARS 



45 



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

 cumstances, into two or man)- 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 relativety high osmotic pressure, although for solutions of 

 equal strength this is greater in the case of the monosaccharides 



Fig. 



21. — Sphere-crystals of inulin [In.] in the cells of the tuberous root 

 of a Dahlia. 



than in that of the disacchaiides. 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 {Sacchariim officiiianim), and in the Sugar Maple 

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

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



