THE STRUCTURAL FEATURES OF CELLULOSE 83 



impossible at present to estimate the degree of randomness in the non- 

 crystalline fraction of the wall. It is, in fact, by no means certain that 

 any of the numerous methods at present used (19, see references in 32) to 

 estimate the amount of non-crystalline cellulose give values of any 

 precision. For one thing, it cannot be expected that two different 

 methods will give the same answer. Thus chemical methods which 

 involve removal of the non-crystalline fraction may well give figures 

 which are too low (if only the more loosely arranged chains are re- 

 moved) or too high (if the less random chains are also attacked, since 

 this may also involve some of the chains on the outside of the crystal- 

 lites). Physical methods will yield results which are therefore at first 

 sight more rehable, but these again will depend on the property chosen 

 as basis. Thus density determinations will give a figure which will be a 

 function of the looseness of packing; refractive index determination 

 will depend both on the looseness of packing and on the degree to which 

 the chains outside the crystallites proper are arranged parallel; and 

 estimates by the X-ray method used by Hermans will obviously include 

 in the non-crystalline fraction all chains which are not regularly spaced, 

 whether they are parallel or not. 



The Intermicellar System 



Nevertheless it is possible to speak roughly of micelles and inter- 

 micellar spaces provided always that the implications of these terms are 

 clearly understood, and this is especially useful perhaps when deaUng 

 with raw botanical material. Most, if not all, of the stains used in 

 dealing with cell walls stain the intermicellar material and not the 

 micellar fraction. Staining methods were in fact used quite early in an 

 attempt to estimate the relative surface area of the micelles at the time 

 when these were thought of as discrete particles. Thus the absorption 

 of methylene blue, impregnation with gold and silver and even the 

 adsorption of water have all been shown to give results in general 

 agreement with the existence in cellulose of crystallites about 50 A. or 

 60 A. in diameter (33). 



In some natural celluloses, and in many celluloses under special con- 

 ditions, it is in fact probable that intermicellar spaces occur in the 

 original sense of the word, i.e. spaces free of cellulose. Thus in the 

 heavily siHcized haulms of grasses, Frey-Wyssling showed many years 

 ago (34) that, if the cellulose is removed, then the remaining matrix of 

 silica behaves optically as though it were permeated by a series of narrow 

 channels lying parallel to each other. This picture arose in virtue of the 

 fact that such a matrix showed the form-double refraction mentioned 



