86 METHODS IN PLANT HISTOLOGY 



ment 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 chloroiodide 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 mem- 

 branes 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 15-30 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 (po- 

 tassium 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 swell- 

 ing. 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. Sulphuric acid changes 

 calcium oxalate into calcium sulphate. When treated with barium 

 chloride, crystals of calcium sulphate become covered with a granular 

 layer of barium sulphate, while crystals of calcium oxalate are not 

 affected. 



Calcium carbonate, when treated with hydrochloric acid or acetic 

 acid, dissolves with effervescence. The acetic acid should be rather 

 dilute. 



