40 



THE CELL AND PROTOPLASM 



17 



19 



Fig. 17. Dingraiii illustratiiifr cliMiigvs in tlie ui-icnUitiuii uf L-ellulose in a many-layered sceoudary wall. 

 Fig. 18. Transverse section of wall, photographed in polarized light between crossed Nicols (x 1400). 

 Fig. 19. Diagram illustrating a many-layered secondary wall. The stipjiled layers are non-cellulosic 



and truly isotropic. 

 Fig. 20. Differentially stained, transverse section of such a wall, photograplu'd in ordinary light. The 



dark layers are non-cellulosic (xl830). 



