504 PRACTICAL BOTANY 



cutting sections, in a mixture of equal parts of alcohol and 

 glycerine. 



Alkanna (the root of Anchusa tinctoria) is used as a test for 

 resin (p. 65), caoutchouc and oils (p. 223). The alcoholic 

 solution of alkannin, as supplied by the dealers, may be used for 

 this purpose ; but it is found better to use sections of the dry 

 alkanna root, as described 011 p. 66. The substance alkannin is 

 not readily soluble in alcohol : the best way to prepare it is to 

 make a saturated solution in absolute alcohol, and then dilute 

 with strong methylated spirit : it is, however, obvious that, as 

 resins are soluble in alcohol, the globules of resin which it is 

 desired to stain are liable to be dissolved on application of the 

 reagent. 



Ammonia. The solution in water is often used for clearing 

 preparations instead of potash, as its action is less intense. It is 

 used with nitric acid as a test for proteids, and with copper sul- 

 phate as a solvent for some forms of cellulose (see below, Copper 

 Sulphate). 



Ammonium Molybdate, used, dissolved in a strong solution of 

 ammonium chloride, as a reagent for the detection of tannin, with 

 which it gives a voluminous yellow precipitate. 



Aniline Sulphate and Chloride are used as reagents for 

 lignified cell-walls, which they stain yellow, while no other parts 

 of the tissue are coloured by them. A saturated solution of 

 either of these substances is made in distilled water, filtered, and 

 a few drops respectively of sulphuric or hydrochloric acid are 

 added, so that the solution shall give a distinctly acid reaction : or 

 a solution may be made in alcohol, and then be diluted with water. 



Aniline Violet (Hanstein's). This is prepared by dissolving 

 equal parts of fuclisin and methyl-violet in alcohol. It stains 

 cellulose cell-walls of a faint violet colour, and lignified cell-walls 

 deep violet. It is especially useful for bringing out the different 

 parts of the bast, since the bast-fibres stain red, whereas the sieve- 

 tubes and the parenchyma scarcely stain at all. The protoplasm 

 is stained pink : amyloid substances, gums, and nuclei stain 

 different shades of red, resins blue, and tannin brick-red. 



Asparagin, A saturated solution of this substance in water 

 is used as a test for asparagin which has been already precipitated 



