X. THE CHEMICAL CONSTITUENTS OF PLANTS 187 



the action of unorganised ferments or enzymes, e.g., diastase, ptyalin, 

 invertase, or by boiling with water and a little acid. 



Cane Sugar, Saccharose, Saccharobiose, C ]2 H 22 O n , the most 

 important sugar, occurs in many plants ; in large quantities in the 

 sugar-cane, in the maple, in beetroot and in sorghum cane. The 

 juice of the sugar-cane (Saccharum officinarum) contains from 16 to 

 18 per cent, of its weight of sugar. Beets contain from 7 to 16 per 

 cent. Cane sugar is also present in the juice of unripe maize, in 

 many palms, in many roots, e.g., turnips and mangolds, in the sap of 

 the lime and birch, in the nectar of flowers, and, mixed with glucose 

 and fructose, in many fruits. 



Commercial sugar is chiefly prepared from the sugar-cane, the 

 beet and the sugar-maple. The properties of sugar are well known 

 and need not bo described here. It melts at 160, and at 190 or 200 

 changes to a brown uncrystallisable substance known as caramel, 

 used in colouring. It does not reduce copper salts. Boiled with 

 dilute acids or by the action of certain ferments, it is converted into a 

 mixture of glucose and levulose (inversion). It combines with lime and 

 baryta to form sparingly soluble saccharates, e.g., C 1 . 2 H 22 O 11 .CaO.2H 2 O 

 and C 12 H 22 O n .3CaO. These substances are decomposed by carbon 

 dioxide, yielding a metallic carbonate (insoluble) and sugar. Cane 

 sugar in plants is mainly contained in the stalks, while the hexoses 

 occur chiefly in the fruits. 



Milk Sugar, C 12 H 22 O n + H 2 O, will be described in Chap. XV. 



Maltose, Malt Sugar, Maltobiose, C 12 H 22 O n + H 2 0, is formed 

 by the action of diastase upon starch, dextrin being simultaneously 

 produced. Maltose is a crystalline substance which undergoes fer- 

 mentation under the influence of yeast, being first converted by an 

 enzyme, maltase, present in the yeast or malt, into glucose. It 

 reduces copper solutions and in most of its properties closely re- 

 sembles glucose. It is probably the form in which starch and other 

 carbohydrates undergo translocation in plants. 



The other disaccharoses are less important. 



Trehalose, C 12 H 22 O n + 2H 2 0, has been found in many fungi and 

 in ergot of rye. 



Melibiose is obtained from the trisaccharose, ramnose, by hydro- 

 lysis with dilute acids or certain yeasts. By hydrolysis it is hydro- 

 lysed into glucose and galactose. Melibiose is not hydrolysed by 

 maltase, invertase, or lactase but is by emulsin or by an enzyme, 

 melibiase, which is present in bottom fermentation yeasts but not in 

 top yeasts. 



The trisaccharoses, C 18 H 32 O 1( .. The only member of this group 

 which need be mentioned is Raffinose, which occurs in beets and in 

 other plants. By strong acids, it is hydrolysed into fructose, glucose 

 and galactose, while weak acids yield fructose and melibiose. Inver- 

 tase converts it into fructose and melibiose but emulsin hydrolyses it 

 to sucrose and galactose. Eaffinose resembles cane sugar and has no 

 reducing power. It crystallises in prisms containing three molecules 

 of water. 



It may be regarded as 



