26 PRACTICAL BOTANY 



wails, which are of almost uniform thickness, and are colour- 

 less or slightly yellow : protoplasm is practically absent in this 

 tissure. 



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. 



b. Treat another section with chlor-zinc-iodine : the walls 

 stain yellow or brown. 



c. Treat as above directed (p. 24), 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), and on cooling re-examine : the corky walls, 

 if the reaction be complete, will be found to have lost their 

 definite outline, and to have run together into irregular 

 viscid drops of eerie acid, which is in some measure soluble in 

 the mixture when hot, and is reprecipitated on cooling. 



