CELL-WALLS 37 



zinc-iodine, and observe that the cell- wall stains a more 

 or less distinct blue or a pinkish violet according to 

 circumstances : the protoplasm, of which a small quan- 

 tity may remain in the hairs, stains yellow : compare the 

 results of similar staining in the last chapter (p. 27). 



In some cases the cell- wall turns blue when it is treated with 

 iodine alone ; instances of this are to be found in the cell-walls of 

 the asci of Lichens, the bast in the stem of Lycopodium and in 

 the root of JRuscus, the endosperm of Pcconia^ and the cotyledons 

 of various Leguminous seeds. 



In other cases the characteristic reactions are not given on 

 treatment with clilor-zinc-iodine, or with iodine and sulphuric 

 acid ; instances of this occur in the tissues of young seedlings, of 

 growing-points, of the cambium, and of Fungi. In the case of 

 young tissues it suffices to treat them previously with hydrochloric 

 acid, or with solution of potash for a short time : they then give 

 the reactions mentioned above ; the tissues of Fungi require a 

 long treatment (three or four weeks) with potash. 



e. Mount still another small quantity of the soaked 

 cotton in acid solution of aniline sulphate, and observe 

 that the cell-walls do not stain. 



/. One of the most characteristic reactions of cel- 

 lulose may be observed as follows : 



Prepare an ammoniacal solution of cupric hydrate 

 (see Appendix A) : take, in a pair of forceps, a small 

 quantity of cotton-wool, and immerse it in the fluid : it 

 will be seen that the separate hairs of the cotton lose 

 their identity, coalesce into a gelatinous mass, and are 

 finally dissolved. 



The solution, and antecedent swelling of the walls 

 may be observed on a slide under the microscope if a 

 very small quantity of the cotton-wool be mounted in 

 the solution. 



