Pectocelluloses and Mucocelluloses 217 



a complex acid which is the main constituent of gum-arabic. 

 Gum-arabic yields, on graduated hydrolysis, a complex of 

 glucoses (galactose, arabinose) and a series of arabinosic 

 acids, e.g. C 2 3H 38 O 2 2, and compounds differing from this by 

 + C 6 Hi O 5 . It appears, therefore, generally, that the pectic 

 group are compounds of carbohydrates of varied constitution 

 with acid groups of undetermined constitution, associated to- 

 gether to form molecular complexes, more or less homogeneous, 

 but entirely resolved by the continued action of simple hydro- 

 lytic agencies ; and the pectocelluloses are substances of similar 

 character in which the carbohydrates are in part replaced by 

 n on- hydroly sable celluloses. The general characteristics of the 

 pcctocelluloses are therefore these : they are resolved by boiling 

 with dilute alkaline solutions into cellulose (insoluble) and 

 soluble derivatives of the non-cellulose (pectin, pectic acid, 

 metapectic acid) ; they are gelatinised under the alkaline 

 treatment ; they are ' saturated compounds,' not reacting with 

 the halogens, nor containing any groups immediately allied to 

 the aromatic series. 



Compound celluloses of this kind are enormously diver- 

 sified in composition, structural character, and distribution, 

 and the group, having none of the sharp lines of differentiation 

 and demarcation presented by the lignocelluloses, cannot be 

 handled at all in the same way. 



We must confine ourselves, therefore, to the one or two 

 more definite types which have been investigated. 



Flax. Commercial flax is a mixed product. The bast 

 fibre proper constitutes from 20-25 P- ct> f tne entire stem, 

 and is more or less imperfectly separated from the wood on the 

 one side, and the cortical tissue-elements on the other, by the 

 ordinary processes of retting and scutching. These residues are 

 visible with the naked eye, but are brought into clearer evidence 

 by means of reagents, followed by microscopic examination. 



