338 MICROCHEMISTRY OF PLANT PRODUCTS 



as potassium tartrate, in which case the sections should be 

 treated with a mixture of 25 volumes of a concentrated aqueous 

 solution of magnesium sulphate with 2 volumes of a concen- 

 trated aqueous solution of ammonium chloride and 15 volumes 

 of water. In this case a crystalline precipitate of ammonio- 

 magnesium phosphate is formed. 



Calcium Oxalate, CaC 2 O 4 . Crystals of calcium oxalate 

 occur so commonly in plants that it is safe to assume that any 

 crystals observed in fresh tissues are of this substance until 

 the contrary is demonstrated. The crystals may occur singly in 

 the cells, in which case their definite crystalline form can be made 

 out, or in the form of agglomerated star-shaped clusters of 

 crystals, or in bundles of parallel needle-shaped crystals, or 

 they may occur very numerously in cells in the form of very 

 minute crystals. The crystals are insoluble in water and acetic 

 acid, but dissolve without effervescence in hydrochloric acid. 

 When they are treated with sulphuric acid, crystals of calcium 

 sulphate are formed in their place. Calcium oxalate appears 

 to be an excretion formed by the union of salts of calcium, which 

 have been absorbed from the soil, with oxalic acid w r hich is 

 formed by the plant. 



Calcium Sulphate, CaSO 4 . Minute crystals of calcium 

 sulphate occur in many desmids. They are insoluble in con- 

 centrated sulphuric acid. A solution of barium chloride dis- 

 solves them with the formation of barium sulphate. 



Callose. The chemical nature of callose is not precisely 

 known; it is supposed by some to be a proteid. Callose occurs 

 in sieve tubes, where it may close up the sieve pores. It also 

 occurs commonly in cystoliths, and in the membranes of pollen 

 grains and various fungi. Callose is insoluble in water, alcohol, 

 and cuprammonia, but is is readily soluble in cold sulphuric 

 acid, calcium chloride, and concentrated chloride of zinc. It 

 is insoluble in cold alkaline carbonates, but swells up without 

 dissolving in ammonia. Corallin, aniline blue, and a mixture 

 of soluble blue and vesuvin, or of vesuvin and orseillin, are 

 suitable stains for callose. The corallin should be dissolved 



