78 Methods in Plant Histology 



a treatment with Schultze's maceration fluid, lignified membranes 

 react like cellulose. 



Phloroglucin in a 5 per cent aqueous or alcoholic solution applied 

 simultaneously with hydrochloric acid gives lignified walls a reddish- 

 violet color. The preparations do not keep. 



Cutinized and Suberized Walls.- -These are insoluble in cupram- 

 monia or concentrated sulphuric acid. They are colored yellow or 

 brown by chloro'iodide of zinc, or by iodine and sulphuric acid, when 

 applied as in testing for cellulose or lignin. With alcannin, they 

 take a red color, but the red is not as deep as in case of fats and oils. 

 After soaking in an aqueous solution of caustic potash, suberized 

 membranes take a red-violet color when treated with chloroiodide 

 of zinc. 



If a strong, fresh alcoholic solution of chlorophyll be allowed to 

 act upon suberized membranes for 15 to 30 minutes in the dark, 

 they stain green, while lignified and cellulose walls do not take the 

 stain. The preparations are not permanent. 



A solution of alcannin in 50 per cent alcohol stains suberized and 

 cutinized walls red, but the color may not be very sharp. 



Cyanin can be recommended. First, treat with Eau de Javelle 

 (potassium hypochlorite), which can be obtained ready for use at 

 any drug-store. This destroys tannins, and the lignified walls lose 

 their staining capacity. Make a 1 per cent solution of cyanin 

 (Griibler's) in 50 per cent alcohol and add an equal volume of glycerin. 

 This should show blue suberized walls, while the lignified walls 

 remain unstained. 



Gum, Mucilage, and Gelatinized Membranes.- -These are all 

 soluble in water and are further characterized by their strong power 

 of swelling. They are insoluble in alcohol. A series of forms with 

 various color reactions is included under this heading. 



Crystals. Nearly all crystals which are found in plants consist 

 of calcium oxalate. Crystals of calcium carbonate, calcium tartrate, 

 and calcium sulphate also occur. Calcium oxalate is soluble in 

 hydrochloric acid or nitric acid. It is better to use the concentrated 

 acids. The crystals are insoluble in water and acetic acid. Sul- 

 phuric acid changes calcium oxalate into calcium sulphate. When 



