CELL-CONTENTS AND CELL-WALLS. 67 



(g) In addition to, or instead of, Dahlia tubers, the following 

 may be used for the demonstration of inulin : tuber of Jerusalem 

 Artichoke, root of Dandelion. Cut sections of fresh material, 

 examine in water, then add alcohol, and note the granular pre- 

 cipitate formed in the cells ; on irrigating with water the precipi- 

 tate will be again dissolved. Pieces of the tissue should also be 

 placed in alcohol for a week or more, as directed for Dahlia, in 

 order to obtain the sphere-crystals. 



VI. CELL-WALLS ; MUCILAGES. 



78. Tests for Cellulose. Soak some cotton-wool in 

 alcohol, to remove air-bubbles, and then in water. 



(a) Mount some of the soaked cotton in water, and 

 with high power note that the long hairs are unicellular, 

 with thick colourless walls and scanty remains of the 

 protoplasm. 



(6) Place some in strong iodine solution in a watch- 

 glass for a few minutes, mount in iodine, and note that 

 the walls are stained faint yellow. 



(c) Transfer a little of the iodine-treated material to a 

 drop of 50 per cent, sulphuric acid, and note that the 

 walls swell up and turn blue. 



(d) Treat some of the material with chlor-zinc-iodine 

 (see Appendix) : the walls become blue or violet. 



(e) Mount some in aniline sulphate solution : the walls 

 are not stained this solution is used as a test for lignin 

 ( 79). 



(/) Place some dry cotton- wool in ammonio-cupric 

 hydrate (" cuprammonia," see Appendix), and note that 

 the hairs fuse into a gum-like mass and eventually dis- 

 solve. 



(g) Mount some of the cotton in " cuprammonia " on a 

 slide, and note the swelling of the walls that precedes their 

 solution. 



The blue colour given with iodine and sulphuric acid, or 

 with chlor-zinc-iodine, is the best positive microchemical 

 test for cellulose, and both of these reagents should 



