REFERENCES 253 



of the secondary wall is affected. Microchemical tests apparently 

 indicated that the cellulose in some way becomes modified before 

 the onset of lignification. Lignification is not general in all the 

 fibres in the cross-section of a stem, but occurs somewhat spas- 

 modically in isolated groups and individuals. At no time is 

 lignification uniform along the length of a fibre, and it increases in 

 amount with age and as the stem matures. 



The process of retting was also studied, and the fibres were 

 submitted to the same treatment as in commerce. Retting is 

 primarily due to bacterial decomposition taking place under water. 

 The flax plants are allowed to remain under water till the bark 

 strips away from the central core. After retting the plants are 

 dried and then passed between fluted rollers to break the central 

 woody core. This broken core is separated from the fibres by 

 beating, and finally other impurities are removed by combing. 



The first action of the bacteria is to attack the outer fibres 

 of the stem. The secondary wall is completely decomposed, leaving 

 the tertiary deposits exposed. The degree of lignification of the 

 fibre influences retting to a marked degree. If the fibres be heavily 

 lignified they are not so easily decomposed as less lignified tissues, 

 and two critical points in the production of commercial fibre are, 

 firstly, determination of the time of " pulling " the plants, so that 

 extensive lignification has not taken place, and secondly the deter- 

 mination of the degree of retting, so that the secondary wall has 

 been completely decomposed and destroyed. 



REFERENCES 



1. Acton. Anns. Bot., 28, 433, 1914. 



2. Aldaba. Amer. J. Boi., 14, 16, 1927. 



3. Allen. Proc. Amer. Phil. Soc, 58, 289, 1919. 



4. Anderson. Amer. J. Bot., 187, 14, 1927. 



5. Bagchee. Anns. Bot., 39, 217, 1925. 



6. Blackburn. Brit. J. Exp. Biol., 1, 413, 1924 ; Amer. Nat., 59, 200, 



1925. 



7. Blackburn and Harrison. Anns. Bot., 35, 159, 1921 ; 38, 361, 1924. 



Brit. J. Exp. Biol., 1, 557, 1924. 



8. Bolles Lee. Quat. J. Micr. Sci., 69, 1, 1924. 



9. BowEN. Zeit. Zell. Mik. Anat., 6, 689, 1928 ; 9, 1, 1929. Anns. Bot., 



43, 309, 1929. 



10. Carter. Anns. Bot., 41, 139, 1927. 



11. Castetter. Amer. J. Bot., 12, 270, 1925. 



