CONSTITUTION OF CELLULOSE 157 



hydrochloric acid are coloured red. They are, moreover, 

 turned yellow by exposure to sunlight. 



(&) Pectocelhdoses. The most important example of a 

 pectocellulose is -flax; pectocelluloses occur also in ramie 

 fibre, hemp, and raw cotton. Their outstanding characteristic 

 is that their non-cellulose constituent is a pectic substance ; 

 so that on boiling with dilute alkali they give a product which 

 gelatinizes in cooling, and from which, on the addition of 

 acid, a precipitate of pectic acid (see p. 146) may be obtained. 

 The pectocelluloses are possibly not true compounds, but 

 merely associated deposits of celluloses with hemicelluloses or 

 pectic substances. 



The widely distributed mucocelluloses comprise such sub- 

 stances as quince or salep mucilage ; both these substances 

 while containing a certain amount of inorganic material give 

 on analysis formulae approximating to C 6 H 10 O 5 . On hydro- 

 lysis with dilute acid they yield varying amounts of insoluble 

 cellulose, together with soluble gums and monosaccharides, such 

 as glucose or even a pentose. 



Schwalbe is of opinion that Cross and Bevan's classification 

 is not justified, and considers that these compounds should not 

 be grouped with cellulose at all, but should be regarded as 

 mucilages (see p. 143). 



(c) Adipo- and Cuto-celluloses. Under this heading are in- 

 cluded the constituents of suberized and cuticularized walls. 

 These substances are by some regarded as ester-likecompounds* 

 of cellulose, with fat or wax-like materials, known as suberin 

 and cutin. This view is based upon the fact that suberized 

 walls, if treated first with a solution of potash, turn with 

 chlorzinc iodide a red-violet colour. 



The work of Gilson, f however, tends to show that cellu- 

 lose does not enter into the composition of such walls, for the 

 following reasons : 



1. Cellulose is not attacked by prolonged boiling in a 3 

 per cent solution of potassium hydrate in alcohol ; suberized 

 walls, on the other hand, are dissolved. 



2. Phellonic acid (C 22 H 43 O 3 ) has been isolated from cork, 



* Cross and Bevan : " J. Soc. Dyers and Colourists," 1919, 35, 70. 

 f Gilson; "La Cellule," 1890, 6, 63. 



