346 MICROCHEMISTRY OF PLANT PRODUCTS 



yellow drops by this treatment. A solution of alcannin colors 

 the fats red, but several hours may be required to accomplish 

 this. A solution of cyanin in 50 per cent, alcohol is also a good 

 stain for fats. The sections will not need to lie in this stain 

 longer than half an hour. If the sections are overstained they 

 may be washed out in glycerine or a concentrated solution of 

 potassium hydrate. 



Frangulin, CjoHjqOjq. — This glucoside occurs in the cortex 

 of species of Rhamnus. It forms yellow crystalline masses which 

 are insoluble in water, but soluble in alkalies, which produce 

 with it a cherry-red color. Concentrated sulphuric acid pro- 

 duces with frangulin an emerald-green, which changes into 

 purple, and finally the frangulin dissolves with a dark red color. 

 Water will precipitate it from this solution. 



Fungus Cellulose. — The membranes of very few fungi give the 

 reactions of cellulose. The membranes of most fungi are insol- 

 uble in cuprammonia, and are colored from yellow to brown by 

 chloroiodide of zinc, sulphuric acid and iodine. Neither do they 

 react in the same manner as suberized and lignified membranes. 

 They are, therefore, considered to be a distinct substance, which 

 is termed fungus cellulose. See also under Chitin. 



Gelatinous Sheaths. — The homogeneous gelatinous sheaths 

 which cover the entire outside of certain algae — notably, species 

 of Spirogyra and Zygnema — may be demonstrated by the use of 

 certain stains and other substances, such as India ink, which 

 may become deposited in the sheaths. Aqueous solutions of 

 vesuvin, methyl-violet and methylene-blue will stain both the 

 cell-walls and gelatinous sheaths, but the latter with less intensity. 

 Chloroiodide of zinc will stain the wall without affecting the 

 sheaths. Turnbull's blue may be deposited in the gelatinous 

 sheaths in the following manner: A small number of Zygnema 

 filaments, for instance, may be tied together with a thread and 

 placed for about two minutes in a 2 per cent, solution of ferrous 

 lactate, then quickly washed in water, and transferred to a 0.2 

 per cent, solution of ferricyanide of potassium. A small amount 

 of Turnbull's blue will then be deposited in the gelatinous sheaths. 



