PLANT PRODUCTS 575 



Protoplasmic Connections. The protoplasmic connections between the plates 

 of sieve tubes may be strongly stained by acid fuchsin and aniline water (see page 

 542). More delicate protoplasmic connections require the use of a swelling agent 

 for their demonstration. Sections of fresh material may be fixed with a solution 

 of 0.05 Gm. of iodine and 0.2 Gm. potassium iodide in 15 Gm. of water, and then 

 the iodine should be replaced by chloroiodide of zinc, which should be allowed to 

 act for about 12 hours. At the end of this time the membranes traversed by the 

 protoplasmic connections will be swollen to greater or less extent, so that the chloro- 

 iodide of zinc may be washed out in water and the sections stained by acid fuchsin 

 and aniline water, as already suggested. Sulphuric acid may be used instead of 

 the chloroiodide of zinc as the swelling agent. For demonstration purposes sec- 

 tions through the endosperm of the Gramineae, or tangential sections through the 

 green bark of Rhamnus frangula, may be used. Sections are placed on a cover- 

 glass in a drop of sulphuric acid. After a few seconds the acid is washed away 

 by immersing the cover-glass and moving the sections about in a dish filled with 

 water. The sections remain in the water for only a short time, and are then to be 

 stained in an aqueous solution of aniline blue, washed in water, and mounted for 

 examination in dilute glycerine. Or the sections may be stained in a saturated 

 solution of picric acid in 50 per cent, alcohol, to which aniline blue is added until 

 the solution has a blue-green color. 



Pyrenoids. The pyrerioids may be simultaneously fixed and stained by placing 

 the material in a concentrated solution of picric acid in 55 per cent, alcohol, to a 

 watch-glass of which is added about 5 drops of the acid fuchsin and aniline water 

 solution described on page 542. The material should remain for about 2 hours in 

 a watch-glass of this solution. It should then be washed for a quarter of an hour 

 in alcohol and mounted for examination in dilute glycerine. If permanent mounts 

 are desired, the material should be placed in a watch-glass of dilute glycerine, which 

 should then be allowed to concentrate in a place free from dust. The material 

 should finally be mounted in glycerine- jelly. The material may be mounted in 

 Canada balsam by transferring it from the alcohol in which it was washed to suc- 

 cessively stronger solutions of balsam in xylol until the ordinary solution used for 

 mounting is reached. 



See under Dahlia in the previous chapter for other methods of treating 

 pyrenoids. 



Reserve Cellulose. Those hemicellulose thickenings of cell- walls in seeds, etc., 

 which are essentially reserve food materials, and are made soluble by diastatic fer- 

 ments and employed as food material in the germination of seeds, are known as 

 reserve cellulose. Sections taken from a sprouted date seed and treated 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 tinc- 

 ture 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, C 2 6H 2 8Oi4. This 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 color to the cell-sap of the young roots; the cell- walls of old roots, 



