138 THE CARBOHYDRATES 



It may here be remarked that although the best quality 

 paper is manufactured from cellulose freed as completely as pos- 

 sible from uon-cellulose constituents by the method described 

 below, lignocelluloses are used as such for the preparation 

 of inferior qualities of paper, without previous treatment for 

 the removal of the lignin. Such papers when dipped in a i-^ 

 per cent alcohol solution of phloroglucinol and touched with a 

 drop of diluted hydrochloric acid are coloured red. They are, 

 moreover, turned yellow by exposure to sunlight. 



(b) Pectocelluloses, which occur in fibrous and parenchy- 

 matous tissues of the stems and roots of Phanerogams, are 

 substances in which the non-cellulose constituent is of a 

 colloidal or gummy nature and belongs to the group of sub- 

 stances known as "Pectic Compounds" (see p. 128). Similarly 

 the mucocelluloses which are found in the seeds and fruits of 

 Phanerogams and in Algae contain for their non-cellulose con- 

 stituent substances of a mucilaginous or gummy nature. The 

 chemical characteristics of the pecto- and muco-celluloses are 

 not, however, sufificiently well defined, as yet, to warrant a 

 detailed consideration. 



ic) Adipo- and Ciito-celluloses. — Information regarding the 

 composition of the constituents of suberized and cuticularized 

 walls is very meagre. Till quite recently these compounds 

 have been looked upon as cellulose in association with sub- 

 stances of a fatty or wax-like nature, and 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 * tends to show that cellulose 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 (C2._jH4303) has been isolated from cork, 

 and this substance, together with its potassium salt, gives a 

 red coloration with chlorzinc iodide. This suggests that the 

 coloration of suberized membranes with chlorzinc iodide after 



* Gilson : " La Cellule," 1890, 6, 63. 



