CELL-WALLS 25 



so that it shall not gain access to the stage, or the objective ; 

 only a very small quantity is to be used, and the slide should be 

 washed in water directly the observation has been made. A 

 low power will suffice to show that 



1. The cell-walls swell greatly, and in an irregular form, 



and ultimately lose their sharp contour. 



2. They assume a blue colour. This colouring is often not 



uniform, and this reaction, though trustworthy as 

 positive evidence of the presence of cellulose where 

 the blue colour is obtained, is not secure as proving 

 the absence of cellulose if the blue colour be not 

 seen. 



d. Mount a fresh piece of the soaked cotton in chlor-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 quantity may remain in the 

 hairs, stains yellow. 



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. 



f. One of the most characteristic reactions of cellulose 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. 



These reactions may be repeated on other tissues, e.g. the 

 endosperm of the Date. (See larger edition, p. 38.) 



B. Liernified Walls. 



For the reactions of lignified walls the wood of the Pine will 

 serve : for instance, sections may be cut from an ordinary wooden 

 match. Having cut thin transverse sections, soak them first in 

 alcohol to remove bubbles of air : mount one of them in glycerine, 

 and observe under a high power the very regular network of cell- 



