264 ORGANIC AGRICULTURAL CHEMISTRY 



would also hydrolyze with comparative ease, yielding mono- 

 saccharose products. The cellulose which is present in peas, 

 beans, etc., and in green grasses seems to be a simpler and purer 

 cellulose than the normal fibrous variety, and does in fact dis- 

 solve more easily and hydrolyze more easily than the normal. 

 This form has been termed hemicellulose. Other substances 

 known as mannans, galadans and pentosans (pp. 270, 272) are 

 either identical with hemicelluloses themselves or are contained 

 in them. 



Lignocelluloses. — As the cell walls, especially of the stems, 

 stalks and trunks of plants, become older they take on a special 

 character which is known as woody. They then possess much 

 greater hardness and strength and form the supporting struc- 

 ture of plants. The change in character is due to a change in 

 chemical composition resulting from the infiltration into the 

 original cell wall of noncellulose substances possessing a gummy 

 or resinous nature. These substances are known in general as 

 lignins, and the celluloses formed are called ligno-celluloses. 

 It is probable that these lignins are in actual chemical combina- 

 tion with the cellulose, though it may be that they are simply 

 mixed with it. The exact chemical nature of the lignins is 

 also unknown, but they are undoubtedly of pentosan character. 

 They yield pentose sugars on hydrolysis. While the normal 

 celluloses are the chief source for the manufacture of the best 

 grades of paper, the lignocelluloses of the softer woods, such 

 as spruce, fir, etc., are being used almost exclusively in the 

 manufacture of paper for newspapers and similar uses. In 

 making the paper from wood more or less of the lignins are 

 removed. Cellulose so obtained amounts to about 55 per cent 

 of the weight of the wood itself. (See also Paper, p. 126.) 



Pectocelluloses. Pectins. — Two other kinds of compound 

 celluloses should be mentioned. The first of these is the pecto- 

 celluloses, in which cellulose has associated with it noncellulose 

 substances termed pectins analogous to the lignins of the ligno- 

 celluloses. These pectins, like the lignins, are probably not 

 simple substances, but are of carbohydrate character, perhaps 



