CELLULOSE-PROTEIN COMPLEXES 



235 



The Cellulose of Plant Cell Walls 



The structure of cellulose itself is not without significance in this 

 respect. Classically, cellulose is regarded as a polvmer of /3-D-glucose 

 residues joined in long chains by 1-4 links. Over certain parts of 

 their length these chains lie parallel to each other and regularly 

 spaced in a lattice dimensioned as in Fig. 4, which is now known 

 to be only approximately correct (Honjo and Watanabe, 1958; Pres- 

 ton, 1958). The lattice is such as to yield a more or less well-defined 

 diffraction diagram when a beam of X-radiation or electrons is 



Fig. 4. A unit cell of cellulose after Meyer and Mark. Dimensions are 

 given in Angstrom units. The black circles represent oxygen atoms. 



passed through it. From such diagrams the spacing between promi- 

 nent planes in the lattice may be calculated, and particular note may 

 be taken of the spacings at 3.9, 5.4, and 6.1 A between planes lying 

 parallel to chain direction, and at 2.56 A from planes lying normal 

 to chain direction (Figs. 4, 5). The lattice occurs, of course, inside 

 the microfibril, which therefore contains a number of molecular 

 chains (of the order of 200) lying parallel to its length. 



In general, celluloses isolated from plant cell walls include poly- 

 saccharides containing sugars other than glucose, and it is now 

 known, that these are not always contaminants from the associated 

 amorphous non-microfibrillar comj^onents. In a series of analyses 

 controlled by electron microscope observation of wall extracts, Cron- 



