Microscopic Structure of the Cell Wall 



13 



be detected by applying various stains to the fiber (2, 17) , as well 

 as by direct chemical analysis (29) . When young fibers are purified 

 by the removal of wax and pectin, the delicate framework of cellu- 

 lose always remains. It appears, therefore, that the primary wall 

 is made up of a tenuous network of cellulose embedded in rela- 

 tively large amounts of wax and pectic substances. There is evi- 

 dence which indicates that the structure of the primary wall of 



Fig. 1. Fibers stained with Congo red and photographed between crossed 

 nicols to show the strands of cellulose in the primary wall. A. Part of a 15- 

 day fiber placed at 45° with respect to the planes of the nicols. B. Tip of a 

 3-day fiber placed at 45° with respect to the planes of the nicols. Magnifi- 

 cation X 890. 



cotton is similar to that found in other plant cells (5) . The orienta- 

 tion of the fibrils varies in different cells, diverse types showing, 

 however, a fundamentally similar structure. 



Although the coarser details of the structure of the secondary 

 wall are often visible in unswollen material, the pattern is studied 

 to best advantage in expanded sections. By the use of suitable 

 swelling agents details of structure which could not be detected 

 otherwise, are rendered microscopically visible. Use of the swelling 

 technique in conjunction with X-ray data and polarization studies 

 offers a satisfactory method for observing the structure of the cell 

 wall. 



