20 The Structure of Protoplasvi 



needles, the fine fibrils which comprise the secondary wall can 

 easily be separated from one another (Fig. 7) . 



In the cotton fiber the fibrils are grouped to give a layered pat- 

 tern. In an expanded transverse section they may be observed as 

 more or less round bodies (Fig. 3, A and B) . In the denser layers 

 of the wall there are, presumably, more fibrils per unit area than in 

 the more porous layers which are deposited during the day. 

 Although the secondary wall appears to be resolved into a system 

 of fine fibrils, it is unlikely that the fibrils are uniform and discrete 

 morphological units of constant dimensions. Their presence is, 

 however, indicative of the fibrous structure of the wall and the 

 manner in which it was deposited. 



In the case of a heavily lignified secondary wall, it is possible 

 to remove the cellulose and leave a firmly coherent residue of lignin, 

 and conversely, it is possible to remove the lignin and leave the 

 cellulosic matrix. Following Frey-Wyssling's (13) conception of 

 the submicroscopic structure of cellulose (recently supported by 

 additional evidence from studies involving use of the electron 

 microscope (25) ) , Bailey (6) has suggested a similar configuration 

 for the finer visible structure of swollen secondary walls. Accord- 

 ing to this viewpoint the secondary wall consists of a matrix of 

 cellulose fibrils interpenetrated by a system of interconnecting 

 capillaries which commonly contain pectic substances, hemicellu- 

 loses, lignin, cutin, suberin, and other organic compounds. The 

 visible pattern of a wall may, therefore, be caused by variations in 

 the orientation of the cellulose fibrils, and also by variations in the 

 amount and arrangement of organic substances which are deposited 

 between the fibrils. 



REFERENCES 



1. Anderson, D. B. 1935. Bot. Rev. 1, 52. 



2. Anderson, D. B., and Kerr, T. 1938. Ind. Eng. Chem. 30, 48. 



3. AsTBURY, W. T., AND Preston, R. D. 1940. Proc. Roy. See. B 854, 54. 



4. Bailey, I. W., and Kerr, T. 1935. Jour. Arnold Arboretum 16, 223. 



5. Bailey, I. W. 1938. Ind. Eng. Chem. 30, 40. 



6. Bailey, I. W. 1939. Bui. Torrey Botanical Club 66, 20. 



7. Bailey, I. W. 1940. The Walls of Plant Cells in "The Cell and Protoplasm," 



Lancaster, The Science Press. 



8. Balls, W. L. 1922. Proc. Roy. Soc. B 93, 426. 



9. Balls, W. L. 1923. Proc. Roy. Soc. (London) B 72, 72. 



10. Balls, W. L. 1928. Studies of Quality in Cotton, Macmillan & Co., Ltd., 



London. 



11. Berkley, E. E. 1939. Textile Research 9, 355. 



