MICROSCOPIC TECHNIQUE AND REAGENTS. 761 



or an acidified alcoholic solution. This solution gives to cellulose, 

 lignin and the protoplasmic cell-contents a violet color. 



IODINE AND POTASSIUM-IODIDE SOLUTION consists of iodine, 

 2 Gm. ; potassium iodide, 6 Gm. ; water, 100 c.c. 



IODINE WATER is prepared by adding as much iodine to dis- 

 tilled water as it will dissolve (about i : 5000). 



CHLORAL-IODINE SOLUTION consists of a saturated aqueous 

 solution of chloral, to which iodine is added. This reagent is 

 useful for staining the starch grains in the chloroplasts. 



PHLOROGLUCIN SOLUTION, used as a test for lignin, is a 0.5 

 to 2 per cent, alcoholic solution of phloroglucin, which is used 

 in conjunction with hydrochloric acid. The reagent should be 

 protected from light. 



IRON SOLUTIONS are aqueous or alcoholic solutions containing 

 5 to 20 per cent, of ferric acetate or ferric chloride. These are 

 mostly used as tests for tannin, giving either a bluish-black or 

 greenish-black coloration or precipitate. 



COPPER-ACETATE SOLUTION is a 7 per cent, aqueous solution 

 of cupric acetate. It is the most distinctive test for tannin, par- 

 ticularly with fresh material, producing a reddish-brown precipi- 

 tate in the cells containing tannin. The fresh material should be 

 cut into small pieces and immediately placed in the solution of 

 copper acetate and allowed to remain for from 24 to 48 hours. 

 The excess of the reagent is then washed out and the material 

 placed in alcohol. 



SCFULZE'S MACERATING SOLUTION is prepared by adding 

 crystals of potassium chlorate from time to time to warm con- 

 centrated nitric acid. It is employed in the isolation of lignified 

 cells. The material is allowed to remain in the solution for a 

 short time or until there appears to be a disintegration of the 

 tissues. A large excess of water is then added. The material is 

 carefully washed, the cells teased apart and mounted in a solution 

 of methylene blue. 



SPECIAL REAGENTS comprise all those substances which are 

 employed in the morphological study of the cells, and include 

 solutions of the alkalies (o.i to 6 per cent.) solutions of the 

 mineral acids, which may be weak or concentrated, and solutions 

 of organic acids, as acetic and citric. 



