On Cell-wall Structure as seen in Cotton Hairs. 



427 



being stressed enormously, under a cover-slip, by pressing with the blade of 

 a knife. This we have found very useful ; it is evidently akin to the breaking 

 of aeroplane timber studied by Robinson.* 



(d) The inter-relation of external convolutions and internal wall structures 

 has been systematically examined by detailed repeated mapping along the 

 length of single hairs. 



(e) Groups of hairs of equal length from single seeds have been similarly 

 mapped to obtain the average distribution of convolutions in studying the 

 change from day to day in dated samples. A very full re-examination of the 

 daily pickings samplesf has also been made in connection with this work 

 but only slight use will be made of these results at present, as they need 

 direct experiment on growing plants for confirmation of our interpretations. 



The evidence on which we base our conclusions is very detailed and 

 various, and to particularise every item would be extremely tedious. We 

 have, therefore, adopted the plan of summarising our results rather after the 

 manner of geological research ; and by way of further assistance in keeping 

 this note from undue expansion, we shall restrict ourselves to dealing with 

 the more debateable features of hair structure as brought out by Mr. Denham's 

 memoir, already referred to. 



The Cuticle. 



This we found to be distinct from the primary wall, though extremely 

 tenuous. It possesses a spiral structure, probably showing reversals of the 

 spirals, and quite probably identical in frequency, or even in details of 

 pattern, with the pit spirals (see below), but the difficulty of correlating the 

 two sets of observations is very great ; Haller's method^ (SnCl 2 and AUCI3) 

 was not successful. The spiral lines of weakness and their apparent reversals, 

 plus the resistance of the cuticle to solvents, determine the familiar " beading " 

 of swollen hairs. The miscalled " stomata " of De Mosenthal§ are probably 

 primary wall-structures in essence, the cuticle being moulded to them ; we 

 doubt very much whether the cuticle is actually perforated. A granular 

 superficial structure seen after heating (in the thiocyanate process) and 

 staining with osmic acid seems to be due to the melting and redistribution of 

 the wax film, which varies in amount with varieties and species of cotton 

 around 04 per cent, of the hair weight. 



* Robinson, W., " The Microscopical Features of Mechanical Strains in Timber and 

 the Bearing of these on the Structure of the Cell-wall in Plants," ' Phil. Trans.,' B, 

 vol. 210, p. 49 (1920). 



t W. L. B., "Raw Cotton," p. 112, loc. cit. 



% Haller, 'Chem. Zentr.,' p. 652 (1920). 



§ De Mosenthal, H., " Observations on Cotton and Nitrated Cotton," ' Jour. Soc. 

 Chem. Ind.,' vol. 23, p. 292 (1904). 



