CYTOKINESIS AND THE CELL WALL 



179 



fiber is dried and farther apart when it is swollen (Frey). Presumably 

 the valencies binding the units into chains offer greater resistance to 

 swelling forces than do those uniting the chains laterally; hence a cellulose 

 fiber swells unequally in different directions. Sponsler and Dore have 

 shown that mercerization involves a lateral shift of the chains in the 

 wall and a partial rotation of their units, together with certain other 

 changes. The precise nature of the structural changes occurring as the 



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Fig. 104. — Diagrams of cell-wall structure as indicated by X-ray analysis. A, large 

 micellse with chains of glucose residue units showing in one of them, a, primary valence 

 forces; 6, secondary association forces; c, tertiary micellar forces. {After Scifriz, 19296.) 

 B, minute portion of cell wall in perspective, showing portions of six chains, each consisting 

 of three glucose residues (large circles) and their connecting oxygen atoms (small circles). 

 (After Spo?isler, 1931.) C, inner surface of wall; four chain molecules with four glucose 

 units shown in each. Black circles and white circles represent oxygen atoms and carbon 

 atoms, respectively; hydrogen atoms not shown. {After Sponsler, 1929.) 



wall grows in area and becomes impregnated with other substances, 

 such as lignin, remains to be determined. 



It is a suggestive fact, as pointed out by Sponsler, that about the only 

 solid materials deposited in large amounts by plant protoplasm, namely, 

 cellulose and starch, consist of CeHioOa units arranged in patterns. 

 There is similar evidence that certain animal products, such as chitin, 

 hair, and silk, have their molecules arranged in regular patterns. -^ It is 

 possible that this is due not only to the chemical properties of protoplasm 

 and the forces of crystallization but also to certain structural features in 

 protoplasm itself. Seifriz (19296) has emphasized the idea that the 

 contractility, cohesiveness, elasticity, and tensile strength of protoplasm, 



" Herzog and Jancke (1921), Brill (1923), Astbury and Street (1931), Astbury and 

 Woods (1932). 



