X. 



THE CHEMICAL CONSTITUENTS OF PLANTS 



183 



HCOH 

 HOCH 



GH.,OH 



CH,OH 



Trehalose = glucose and glucose. 



It will be noted that maltose and lactose still retain the aldehydic 

 function, for the groups enclosed in dotted lines easily pass, by a. 

 wandering of the hydrogen atom of the hydroxyl to the third next 

 carbon atom, into a true aldehyde group, and are therefore possessed 

 of reducing powers, but in sucrose and trehalose there are neither 

 aldehyde nor ketone groups and so these latter sugars are non-reducing. 



III. Trisaccharoses, C 18 H 32 O 1(3 . Several have been prepared, but 

 the only one which need be mentioned here is Raffinose which 

 is a compound of galactose, glucose and fructose and is strongly 

 dextro-rotatory. It possesses no reducing action and, by acids, is 

 hydrolysed first into melibiose and fructose and finally into glucose, 

 galactose and fructose. 



IV. Tetrasaccharoses, C^H^O^. 



Stachyose is a combination of fructose, glucose and two molecules 

 of galactose. 



Y. Polysaccharoses, (C fi H 10 O 5 ) w . These are complex bodies re- 

 sulting from the combination of large numbers of molecules of the 

 monosaccharoses, but whose constitution and molecular weights are 

 unknown. The more important divisions are the polypentoses or 

 pentosans and the polyhexoses or hexosans, but intermediate sub- 

 stances, i.e., compounds containing both pentoses and hexoses, are also 

 known. 



The following are important polysaccharoses : 



Starch. 



Dextrin. 



Glycpgen. 



Inulin. 



Levulin. 



Cellulose. 



Gums. 



Eesembling the carbohydrates in character are many other com- 

 pounds occurring in plants. Among these may be mentioned : 



