70 CELL-CONTENTS AND CELL-WALLS. 



fluid. Put into the solution some rather thick sections of 

 cork, and boil for a short time the sections lose shape 

 and fuse into a mass ; on cooling, pour off the solution 

 and replace it by alcohol the mass is dissolved. 



(c) Make this experiment with thin sections, taking 

 great care not to let the acid fumes injure the microscope. 

 Warm the sections gently with a little maceration fluid on 

 a slide, and note that the corky walls turn bright yellow ; 

 then boil the liquid on the slide, allow to cool, and note 

 that the walls have fused into drops (consisting of eerie 

 acid). 



(d) Corky walls also turn red with alkannin, but not so 

 deeply as in the case of oils for which alkannin is also 

 used as a test. 



81. Cutiuised Walls resemble corky walls in their 

 general reactions. If sections of stems, etc., are placed 

 for an hour or so in strong freshly-made chlorophyl^ 

 solution, the cutinised and the suberised walls are stained 

 deeply green, while lignified and cellulose walls remain 

 unstained. Cutin is typically developed in the outer walls 

 of epidermal cells, which often show a stratified clear or 

 yellowish cuticle. 



82. Gums and Mucilages may be treated here, since they are 

 often, though not always, derived from cell- walls. They are greatly 

 swollen by potash, dissolve in water, and are insoluble in alcohol. 

 Vegetable gums may or may not give the same reactions as ordinary 

 cellulose ; they are stained deeply blue with methylene blue and 

 in some cases Hoffman's blue, pink with corallin-soda. Most of 

 these bodies are allied to carbohydrates ; they are converted into 

 dextrin by treatment with sulphuric acid ; on treatment with nitric 

 acid they yield oxalic and mucic acids ; and they are quite amor- 

 phous, not being crystallisable like the sugars. 



(a) Examine commercial gum-arabic (obtained from an Acacia). 

 (1) Treat with warm water it dissolves ; (2) add alcohol to the 

 solution it is precipitated ; (3) treat with iodine brown colour ; 

 (4) treat with sulphuric acid and then with iodine brown colour. 



(6) Soak seeds of Linseed in water for an hour or so, and note 

 that the surface of the seed is covered by a thick transparent gum. 

 ( 1 ) Cut transverse sections of a dry seed (wet the razor with alcohol 



