X. THE CHEMICAL CONSTITUENTS OF PLANTS 189 



Dextrin, (C ( .H 10 O 5 ) 4ft (?). By the action of dilute acids in the cold, 

 by the limited action of diastase (the ferment found abundantly in 

 malt, etc.) upon starch paste, or by the action of a temperature of 

 210 to 280 upon dry starch, dextrin is produced, a substance easily 

 soluble in water and giving no blue with iodine solutions. 



Amylo-dextrin, with the composition C 12 H. 72 O 11 .12C 6 H 10 Or i (i.e., 

 consisting of one group of maltose and twelve of dextrin), malto-dextrin, 

 C 12 H 22 11 .4C 6 H 10 Or i , and other intermediate products are formed. 

 They have been examined and described by Brown and Morris. 1 



Commercial dextrin or " British gum " is obtained by heating 

 starch to 210 or higher, or by moistening starch with a mixture of 

 nitric and' hydrochloric acids and heating it to 100 or 125. It is 

 used as a substitute for gum arabic and probably is a complex 

 mixture. 



Dextran or fermentable gum, found in beetroots, is amorphous, 

 soluble in water, and can be converted into dextrose by boiling with 

 dilute acids. 



Lichenin, found in Iceland moss, is soluble in hot water, but sepa- 

 rates in flocks on cooling. 



Glycogen, (C 6 H 10 05) nt occurs in the liver and many other parts of the 

 animal, and is present in certain fungi. It is a white powder, having 

 a composition (C 6 H 10 5 ) 2 .H 2 O, and losing its water at 100. It is 

 soluble in water and gives a red colour with iodine. By the 'action of 

 acids it is converted into dextrose, and diastase converts it into dex- 

 trin, maltose and dextrose. 



Inulin, (C 36 H 62 31 ) 2 , or (C 6 H 10 O 5 ) 12 + 2H 2 O occurs in many plants, 

 particularly in tubers of dahlias and Jerusalem artichokes and the 

 roots of dandelion and chicory. It is a white powder, soluble in hot,, 

 but nearly insoluble in cold water or in alcohol. It is not coloured 

 blue by iodine, and by the action of dilute acids is converted into levu- 

 lose. According to Brown and Morris, 2 its molecular weight is 1980,. 

 corresponding to the formula above given. By the action of heat, 

 inulin forms substances similar to the dextrins. On hydrolysis it yields 

 fructose. 



Levulin, (C 6 H 10 5 ) n , occurs associated with inulin in dahlias and 

 artichokes. It is also found in immature grain, particularly in rye and 

 in oak bark. It is an amorphous, deliquescent substance, yielding a. 

 mixture of dextrose and levulose by treatment with acid. 



Triticin is a similar substance found in couch-grass. Other sub- 

 stances obtained from different sources have been described, but their 

 individuality is not very marked. 



Cellulose is the substance which constitutes the main portion of 

 the frame- work o plants. It occurs in numerous forms, and in plants 

 is always mixed or combined with other products of growth, from which 

 it can usually be separated by taking advantage of its inertness and re- 

 sistance to most reagents. By treating the plant tissues with chlorine, 

 boiling with alkaline solutions, washing, treating with dilute acid, 

 water, alcohol and ether, a residue of nearly pure cellulose is usually 



1 Jour. Chem. Soc., 1889, Trans., 449. z lbid. t 464. 



