178 INTRODUCTION TO CYTOLOGY 



between the old ones ("intussusception theory"). Similar to this was 

 the later view of Wiesner, mentioned in the preceding paragraph. Stras- 

 burger held that the units are not micellse but single molecules linked 

 together in a reticular framework by their chemical affinities. He 

 attributed growth in area to simple stretching without intercalation of 

 particles, and growth in thickness to apposition of small "microsomes." 

 The longitudinal or spiral striations observed in many walls were thought 

 by some to indicate a linear arrangement of particles, while the fine 

 lamination of the wall was attributed either to unlike orientations in 

 contiguous lamina or to differences in water content. 



The recent advances in our knowledge of the finer structure of the 

 cell wall have been made largely through studies of diffraction patterns 

 produced when X-rays^° are passed through cellulose and of the effects 

 obtained with polarized light. ^^ These studies, notably those of Sponsler 

 taken together with the chemical researches of Irvine, have shown that 

 the primary structural unit in the wall is an anhydrous glucose residue 

 with the formula CeHioOs. Such units are bound together in cellulose 

 chains by primary valencies, while the chains are in turn linked laterally 

 by secondary valencies in such a way that the units form a regular 

 three-dimensional space lattice (Fig. 104). In other words, the wall has 

 a crystalline structure. In the fibers of ramie {Boehmeria nivea) and the 

 Valonia cell wall, the distance between the centers of adjacent units is 



o o 



calculated to be about 5.15 A. longitudinally, 6.1 A. tangentially, and 



o 



5.4 A. radially (Sponsler). There is also evidence that the chains are 

 aggregated into bundles, or colloidal micellcB, these probably being 

 between 100 and 600 A. (0.01 to 0.06^) long and between 20 and 50 A. 

 (0.002 to 0.005/x) thick. The nature of the matter between these micellse, 

 or "crystallites," is unknown. 



In a given visible layer of the wall there are many layers of primary 

 units, and the chains they form may be arranged parallel to the longitu- 

 dinal axis of the cell (ramie), or more or less obliquely (cotton). In 

 Valonia there are two main sets of chains which usually cross each other 

 at an angle of about 80°. This structure extends through the many- 

 layered wall. The chains are found to be parallel to the fine striae visible 

 on the surface of the wall. There are many facts which indicate that 

 it is not the surface upon which a layer is deposited that determines the 

 arrangement of its elements. It is reported that in the cotton fiber the 

 crystalline pattern becomes more perfect as the fiber matures (Clark 

 et al.). The micellse evidently come to be much closer together when a 



20Herzog and Jancke (1919-1920), Sponsler (1925a6, 1926, 1928a6, 1929, 1931; 

 general account, 1933), Sponsler and Dore (1926, 1928), Bragg (1930), Clark, Pickett, 

 and Farr (1930), Astbury, Marwick, and Bernal (1932). See Frey (1926a), Meyer 

 and Mark (1928), and Seifriz (19296). 



21 Balls (1923), Frey (19266, 1927, 1928), Preston (1931), D. B. Anderson (1927), 

 Mitchell (1930), M. Shaw (1929). 



