Pectocelluloses and Mucocelluloses 221 



stituents is as yet quite unknown, and we have therefore none 

 but the general basis of classification. 



In the same way also the parenchymatous tissue of fruits, 

 fleshy roots, &c. the typical pectocelluloses must be, for 

 the present, dismissed with the bare mention. 



The investigation of these substances belongs rather to the 

 province of general carbohydrate chemistry than to the 

 narrower cellulose group ; and the problems involved are in 

 many respects rather morphological and physiological than 

 purely chemical. 



These same considerations apply also in great measure to 

 the mucilaginous constituents of plant tissues, though certain 

 of these have been investigated by modern chemical methods. 

 The relationship of these substances to cellulose is indicated 



(a) by the histology of the tissues, which shows them to be 

 associated with the cell wall^ rather than with the cell contents ; 



(b] by their empirical composition, which is approximately that 

 of cellulose ; (c) by their reactions with iodine, by which they 

 are coloured variously from blue to violet, as are the hydrated 

 modifications of cellulose (Sachsse, Farbstoffe, &c. p. 161). 

 Beyond superficial observations of reactions (iodine) and 

 gelatinisation with water, these compound celluloses which 

 may conveniently be termed mucocelluloses had been but 

 little investigated (Sachsse, loc. cit.) until the systematic work 

 of Kirchner and Tollens, and Gaus and Tollens (Annalen, 

 175, 205 ; 249, 245), upon the mucilages and gums. Of these 

 typical researches we give a brief account. 



(i) QUINCE MUCILAGE was prepared by digesting 50 grms. 

 with i litre of warm water, pouring off, and repeating the 

 digestion ; filtering the mucilage by squeezing through cotton 

 cloth, and precipitating the dissolved product by the addition 

 of hydrochloric acid and alcohol. After washing with alcohol 

 and ether the product was dried, forming brittle fibrous masses ; 



