THE COTTON HAIR 



243 



previously treated with strong acid or alkali. Etiolated stems 

 require a short treatment with aqueous alcoholic potash before the 

 normal colour reactions are given, whereas the normal green stem 

 gives a blue colour with iodine and sulphuric acid without any such 

 preliminary treatment, and only a short treatment is required 

 before the reaction is given with chloriodide of zinc. The claim is 

 put forward that the reaction in the apical region is masked by 

 the presence of other substances, e.g., proteins, and the presence of 

 these bodies prevents 

 the reaction with 

 iodine and sulj)huric 

 acid. Wood, how- 

 ever, has been un- 

 able to confirm this 

 statement. She used 

 the chloramine re- 

 action which depends 

 on setting iodine 

 free from potassium 

 iodide after a pre- 

 liminary treatment 

 of the tissue with 

 chlorine gas. Various 

 plant tissues, both 

 monocotyledons and 

 dicotyledons, were 

 submitted to this 



(1) 





(2) 



Fig. 81.— (1) Development of cotton hair from 

 seed coat. One day after opening of flower. 

 (2) The same, three days later. (From 

 Denham, Shirley Inst. Mem.) 



treatment, and in no case did the experiments indicate more than 

 0-001 per cent, of protein in the cellulose walls. It is therefore 

 unlikely that their presence in the wall will interfere with the 

 normal reactions for cellulose and pectin. According to Wood, the 

 chemical state of the cell wall partakes of an equilibrium between 

 cellulose proper, oxy cellulose and hydrocellulose, and in most cases 

 the two former predominate. 



The Cotton Hair. The economic importance of the cotton hair 

 has led to extended observations on its morphological nature. 

 According to Balls, the ordinary epidermal cell of the outer ovule 



