360 MICROCHEMISTRY OF PLANT PRODUCTS 



with potassium hydrate and stained with alizarine show the 

 inner layers of the cell-walls which have been acted on by the 

 diastase unstained, while the outer layers which have not yet 

 been affected by the diastase are stained an intense violet. If 

 Congo-red is used instead of the alizarine, the intact layers are 

 scarcely stained, while the layers which have come under the 

 influence of the diastase are stained a dark red. See under 

 Hemicellulose. 



Resin. — When sections containing resin are treated for 

 some time with a tincture of alcannin, the resin assumes a red 

 color. When sections from tissues which have lain for about 

 a week in a concentrated aqueous solution of copper acetate 

 are examined under the microscope, the resin will be seen to 

 be colored an emerald green. 



Ruberythric Acid, CjjHjgOi^.— This glucoside occurs in 

 the roots of Rubia tinctorium, and is the chief constituent of 

 the madder dye obtained from the roots of this plant. It gives 

 a yellow colof to the cell-sap of the young roots; the cell-walls 

 of old roots, however, have absorbed it and are colored by it. 

 It is colored a purple-red by potassium hydrate, and an orange 

 color by acids. In dry roots it takes on the form of red flakes, 

 and in the injured cells of fresh material it assumes the same 

 form. It may be extracted by alcohol from its yellow solution 

 in uninjured tissues, but in the red flake form it is not dissolved 

 by alcohol. 



Rutin, C^jHjjOjj. — This glucoside is widely distributed in 

 plants. It crystallizes from an aqueous solution in the form 

 of minute light yellow crystals. The yellow color of straw is, 

 in part, due to it. When treated with ammonia or lime-water, 

 rutin forms a deep yellow solution, which turns to brown on 

 exposure to the air. 



Salicin, C^gH^^O^. — Salicin is'^ glucoside which occurs in 

 particular abundance in the cortex of many poplars and willows. 

 It may be dissolved by water, but more readily by boiling water, 

 by aqueous solutions of alkalies, and by acetic acid. It is 

 insoluble in ether. It crystallizes in the form of needles, scales, 



