CELL-CONTENTS AND CELL-WALLS. 83 



sections are not stained by iodine, chlor-zinc-iodine, etc. ; not dis- 

 solved by potash or by acetic acid ; dissolved by nitric acid without 

 evolution of bubbles ; dissolved by sulphuric acid, and then replaced 

 in the cell by small crystals of calcium sulphate. On adding 

 barium chloride, crystals of calcium sulphate become covered by a 

 granular layer of barium sulphate, while crystals of calcium oxalate 

 are not affected by barium chloride. 



(e) Cut tangential sections of the stem of Horsetail, so as to 

 remove the epidermis, mount in water ; note the numerous small 

 projections covering the epidermal cells, and the radiating bands 

 covering the cells around the stomata. Soak a section in nitric 

 acid in a watch-glass for an hour, then ignite it over a flame on 

 platinum -foil or on a cover-glass ; treat the residue with a little 

 acetic acid, mount in water, and note that a siliceous skeleton 

 remains, showing the markings on the epidermis. 



X. METHODS FOR EXTRACTION OF ORGANIC 

 SUBSTANCES. 



96. Extraction of Non-nitrogenous Organic Sub- 

 stances. The chief non-nitrogenous plastic substances 

 can be extracted from plant tissues by the following 

 methods. 



(A) Dry the fresh tissue after cutting stems, roots, 

 etc., into short lengths at a high temperature (100 C. if 

 possible) in an oven until it ceases to lose weight. Reduce 

 the dried material as nearly as possible to powder, using 

 if necessary a hand-mill or domestic chopping-machine, 

 and grinding and pounding the material in a mortar. 

 Then place it in a Soxhlet fat-extracting apparatus ( 97), 

 using ether as the extracting solvent, and boil for some 

 time. Filter, and place the nitrate (ether extract) in a 

 corked bottle labelled A. 



(B) Dry the residue, and place it again in the extrac- 

 tion apparatus, this time using 60 per cent, alcohol, and 

 boil for some time. Filter, and place the nitrate (alcoholic 

 extract) in a bottle labelled B. 



(C) Dry the residue, place it in a bottle, add water, 

 cork, and shake vigorously and repeatedly for some time, 

 and allow to stand for several hours or until next day. 

 Then filter, and place the filtrate (watery extract) into a 

 third bottle labelled C. 



