542 



The Existence of Daily Growth-rings in the Cell Wall of Cotton 



Hairs. 



By W. Lawrence Balls, M.A., Sc.D. (Cantab.), late Fellow of St. John's 



College, Cambridge. 



(From the Reseai-ch Department, Fine Cotton Spinners' Association, Manchester.) 



(Communicated by F. F. Blackman, F.R.S. Eeceived February 25, 1919.) 



[Plates 14-16.] 



From studies of the growing cotton plant in Egypt* the author was led 

 some years ago to the conclusions that the wall of the cotton-seed hair-cell 

 was " probably composed of concentric layers, laid down during the active 

 growth of each successive night, and numbering about twenty-five in all . . . 

 they would thus, at the most, be about 0-0004 mm. in depth, so that their 

 resolution by the microscope is highly improbable without some previous 

 treatment. "f Various methods were tried with the intention of bringing 

 these layers into the limits of microscopic vision, but it was not until five 

 years later that an accidental observation gave the clue to a method by which 

 the limitations of microscope observation may be extended, and these layers 

 made actually visible. 



The observations which followed, demonstrating the existence of con- 

 centric layers in tlie wall of the cotton-hair as well as in the " fuzz-hairs," 

 would have been interesting in any case on account of their bearing on all 

 the physical and chemical problems which this typical cellulose presents. 

 C. F. Cross has insisted on the necessity for considering cellulose problems in 

 terms of " the ultimate fibre,"J but it now seems probable that the ultimate 

 unit components must be the single layers composing the wall of the said 

 fibre. The bare fact of the existence of such layers would have had no 

 particular significance if it could not have been connected with previous 

 precise study of the growth of cocton-hairs. By counting the number of 

 layers in material previously preserved at known dates during the course of 

 those studies, and remembering the cardinal fact that growth is daily 

 arrested by the sunshine effect under Egyptian conditions,! we have been 

 able clearly to show that these layers are actually the growth-rings whose 



* Summarised in ' The Cotton Plant in Egypt,' London, 1912 ; ' The Development 

 and Properties of Raw Cotton,' Loudon, 1915, p. 79 ; " Analyses of Agricultural Yield," 

 'Phil. Trans.,' B, 1915-17, Parts I-IIL 



t ' Raw Cotton,' p. 79. 



X Presidential Address by C. F. Cross, Society Dyers and Colourists, 1918. 

 § "The Physiology of the Cotton Plant," 'Cairo Sci. Jour.,' July, 1910, et. seq. 



