Pectocelluloses and Mucocelluloses 215 



the binding or cementing of the cells together into a compact 

 tissue. But it is important not to confuse effects, even though 

 they may proceed from the same cause. In the lignocelluloses, 

 the view of incrustation of the cells is too often transferred to 

 the chemistry of the cell-substance, which comes to be regarded 

 as composed of cellulose merely overlaid with non-cellulose 

 constituents which mask its reactions. These views, we main- 

 tain, should be kept distinct. 



The morphology of cell formation teaches that with growth 

 a differentiation of a portion of the cell wall takes place, which 

 in the fully developed condition of the tissue constitutes the 

 division of cell from cell and completes their individualisation. 

 A true ' intercellular ' region is then formed, and chemical 

 differentiation no doubt often takes a different course in this 

 region ; but it has not yet been established that differentiation 

 of the cell-substance does not take place simultaneously in the 

 same direction though in lesser degree. In the lignocellu- 

 lose this certainly appears to be the case ; in the pectocelluloses, 

 which we are about to consider, the problem is more difficult to 

 investigate by chemical and microchemical observation, owing 

 to the absence of any well-marked reactions of the pectic 

 compounds. 



We must now give a brief outline of the chemistry of this 

 group. Their characteristic property is that of yielding gela- 

 tinous hydrates, in which they closely resemble the mucilage- 

 yielding constituents of many seeds, fruits, and rhizomes e.g. 

 linseed, the seed of Plantago Psyllium, the roots of Orchis 

 Morio, &c., many of the Salvia species, the fruit of the 

 quince (Cydonia vulgaris), &c. While, however, the empirical 

 composition of the latter is that of the carbohydrates, viz. 

 C ;i H 2m O m , the pectic group are distinguished by empirical 

 formulae with considerably less hydrogen in proportion to the 

 carbon and oxygen, the general approximate formula being 



