LIGNIFICATION. 



37 



which occur in different proportions in different plants and in 

 different parts of the same plant. 



152. Lignin dissolves readily in Schulze's macerating liquid 

 and in potassic hydrate, but not in cuprararaonia, the well- 

 known solvent for cellulose. 



153. By the use of Schulze's macerating liquid a lignified cell- 

 wall can be wholly freed from its incrusting substance, and pure 

 cellulose will be left behind. For control, it is well to employ 

 the tests for lignin given below, both with ordinary wood and with 

 similar specimens which have been treated with this solvent. 



154. Tests for lignin. 1. Salts of anilin. If a lignified 

 cell-wall is subjected to the action of a strong solution of anilin 

 sulphate acidulated with sulphuric acid, or to that of a solution 

 of anilin chloride acidulated with Imlrochloric acid, it will at 

 once turn yellow. The depth of the color depends somewhat 

 upon the strength of the solution. The color is destroyed by 

 alkalies, but is restored by acids. Wiesner, who first applied the 

 foregoing reagents to the detection of lignin, has suggested an- 

 other which is for many cases even more satisfactory ; namely, 

 2. Phloroglucin. In an alcoholic or aqueous solution of this 

 substance (.01 per cent) a lignified cell-wall does not change 

 color ; but if the specimen is slightly acidulated with hydrochloric 

 acid, it becomes violet or purple. 3. Carbolic acid (phenol) 

 and hydrochloric acid. The solution described on page 11 im- 

 parts to lignified cell-walls, when exposed to a strong light, a 

 green color which is very fugitive. Specimens under examination 

 should therefore be watched from the moment that the reagent 

 reaches them. 4. Indol. An aqueous solution is to be replaced 

 under the cover-glass, after it has moistened the specimen thor- 

 oughly, by a little dilute sulphuric acid ; lignified cells will be- 

 come red or reddish-violet. This reagent does not appear to have 



Liqnirtose : soluble in all the solvents mentioned above, but only to a slight 

 extent in water. 



CHEMICAL COMPOSITION. 



According to Franz Schulze, the probable composition of lignin is : Carbon 

 55.55; Hydrogen, 5.83; Oxygen, 38.62. 



