MICROSCOPIC STRUCTURE OF THE CELL WALL 



Charles W. Hock 

 Research Associate oj the Textile Foundation, National Bureau oj Standards, 



Washington, D. C. 



Past discussions on the cell wall (1, 7, 12, 23, 26) have indicated 

 that a detailed knowledge of its structure will aid in the solution 

 of many botanical problems. Although there is a tendency to con- 

 centrate attention on the protoplast as the fundamental unit of the 

 plant, there can be no doubt but that the wall surrounding this unit 

 plays a role of considerable importance in its life. Since deposition 

 of the wall appears to be closely associated with protoplasmic 

 activity, a clear perception of its structure may be helpful in under- 

 standing the structure and behavior of protoplasm. 



The walls of plant cells exhibit diverse structural patterns 

 depending upon the orientation of the cellulose and other constitu- 

 ents of which the wall is composed. Excellent photomicrographs 

 of cell walls which exhibit concentric, radial, ramifying, or even 

 more complex patterns, have already been published (4, 5) . In spite 

 of such differences, walls from various sources show certain simi- 

 larities in structure which appear to be fundamental. Accordingly, 

 a detailed description of the microscopic structure of a particular 

 cell wall may serve as a basis for comparison with other types. 



Because of its economic importance the attention of many investi- 

 gators has been directed toward a study of the cotton fiber. As a 

 result, considerable information concerning the structure and 

 behavior of its cell wall is available. Furthermore, as material for 

 the study of cellulose deposition, cotton fibers possess several 

 advantages. On the day of flowering, or thereabouts, cotton fibers 

 originate as single-celled outgrowths of epidermal cells of the seed 

 coat, and their growth history can be traced daily thereafter. Where 

 fibers arise as part of a complex tissue, as is the case with wood 

 and bast fibers, the time of their origin is unknown, and their 

 development cannot be followed so readily. 



The first evidence of the origin of cotton fibers is the appear- 

 ance on the day of flowering of a swelling on the outer wall of the 

 epidermal cells of the seed coat. The tubular outgrowths thus 



[11] 



