CONSTITUTION AND ARCHITECTURE IN THE CELL WALL 



35 



The specific gravities of dry fibers approximate the calculated 

 density of crystallite regions (1.60±0.05), hence they must contain 

 relatively little vacant space. Upon hydration, inter- and intra- 

 fibrillar spaces increase appreciably, finally becoming a system of 

 fluid-filled cavities. Within the microfibrils, these spaces average 

 10 A in width, but the intermicrofibrillar spaces may be as much 

 as 84 A wide. 



The fundamental ordered structural element of this fibrous 

 system is the elementary microfibril, or micelle. This is the most 

 perfectly ordered unit, 50-70 A wide and at least 600 A long. This 

 unit then corresponds to the crystalline region whose presence 

 is indicated in the wall. The paracrystalline cellulose in the inter- 

 micellar spaces contains molecular chains oriented parallel to the 

 fibrillar axis but lacking complete three-dimensional intramicellar 

 order (Fig. 1). 



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30*' 



Fig. 1. The micellar structure of cellulose. (From Wardrop, A.B. and 



Bland, D.E., The process of lignification in woody plants. Proc. 4th Intl. 



Congress of Biochem., vol. II, p. 93, 1959.) 



Although some fiber cell walls, ramie, for example, consist of 

 cellulose chains oriented almost perfectly parallel to the fiber 

 axis, this condition is not common or typical. 



More common than the true fiber structure is the fiber-like 

 texture in which orientation of molecular chains parallel to the 

 fiber axis is disturbed by random scattering. The optical properties 



