82 
METHODS IN PLANT HISTOLOGY 
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. 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. 
