CELL-WALLS 39 



a. Treat a fresh section with iodine solution, and note 

 that the walls stain distinctly yellow. 



b. Mount a section thus thoroughly stained with 

 iodine in a single drop of sulphuric acid : no blue 

 colour is produced, the walls swell as do the cellulose 

 walls, but their colour is brownish. 



c. Mount a fresh section in chlor-zinc-iodine; the 

 walls stain yellow, with no trace of blue. 



d. Mount another section in acid solution of aniline 

 sulphate : the lignified walls stain yellow. 



By means of the above reactions a lignified wall may 

 be distinguished from a cellulose wall. 



C. Corky Walls. 



Cut thin sections from a piece of common bottle 

 cork : soak them first in alcohol, in order to remove air 

 bubbles, and then in water: mount a thin section in 

 water, or dilute glycerine, and note under a low power 

 the regular arrangement of the tissue, and the thin, 

 pale yellowish or brown cell-walls, with sharp definition 

 and the absence of cell-contents. 



a. Treat a section with iodine solution : the walls 

 stain yellow. 



&. Treat another section with chlor-zinc-iodine : the 

 walls stain yellow or brown. 



c. Treat, as above directed (p. 36), with iodine and 

 sulphuric acid : the walls are yellow or brown, and do 

 not swell, but retain their sharp outline. 



d. Treat a fresh section with Schulze's macerating 

 fluid (see Appendix A), and warm gently at first : the 

 corky walls turn yellow : then boil vigorously (this 

 should be done at some distance from the microscope 

 as the fumes given off are apt to attack the metal), 



