Grmvth-rings in the Cell Wall of Cotton Hairs. 



553 



expectation. Also we have found that scarcely any hairs had begun to form 

 their first rings on the 21st day, so we have either to assume that this hair 

 was extremely early, as well as being abnormal otherwise, or else that we 

 have here a case of dual wall-formation for the first eight days. 



The writer personally inclines to the latter opinion, though the probabilities 

 can just, and only just, be strained to bring the case into category of normal 

 wall-formation ; it seems therefore desirable to put this interesting observa- 

 tion on record. 



. Conclusions. 



The following facts appear to be firmly established as the result of 

 combining these observations with antecedent studies : — that the primary wall 

 of the seed-hairs in cotton contains very small amounts of cellulose ; that the 

 secondary thickening of the wall proceeds intermittently under normal 

 Egyptian field crop conditions, being arrested each afternoon ; that the 

 cellulose of the hair consequently consists of a number of concentric shells, 

 layers, or " growth-rings," each one representing one day's growth, with the 

 exception of that of the primary wall ; and that the so-called fuzz-hairs are 

 analogous with the lint-hairs, though their growth-rings are coarser and 

 more sharply demarcated. The hairs are covered, outside the cellulose of 

 the primary wall, by a cuticle, bearing wax, which is structurally and 

 historically identical with the cuticle of the testa, while it is structurally and 

 chemically distinct from the cellulose. The secondary wall, but not the 

 primary, is traversed obliquely to the hair axis by simple pits which are rarely 

 visible except in the living hair, and to these pits is due. the twisting of the 

 hair and its characteristic convolutions after death. 



In the method employed we now possess a simple kind of ultra-microscopy, 

 applicable to cellulose. The dimensions of the wall of the lint-hair are such 

 that the thickness of each of the 25 growth-rings composing it can only be, 

 at most, about 0'4 much less than the wave-length of sodium light. 



Stimmary. 



The present communication describes the structure of the cellulose wall of 

 the cotton hair, in relation to its development, as a continuation of observations 

 previously published in " The Development and Properties of Eaw Cotton." 



By suitably swelling the cellulose-wall to some five or ten times its initial 

 thickness, under treatments with CSg and NaOH, concentric layering becomes 

 visible in the swollen walls. 



Material of known age and development, fixed in Egypt, was examined by 

 this method and it was found that there is only one thin primary layer while 

 the hair is growing in length, but, that as soon as thickening of the wall sets 



