22 PKACTICAL BOTANY. 



the alcohol extract is poured off and filtered and then evaporated 

 nearly to dryness, until a piece of coarse blotting paper moistened 

 with it and treated with hydrochloric acid turns violet. The 

 extract is then ready for use. It gives a violet colour to lignified 

 cell-walls, as it contains other substances ( especially pyrocatechin) 

 besides phloroglucin. 



Phenol (carbolic acid). Used, together with hydro- 

 chloric acid, as a test for lignin. The best preparation 

 of it is its solution in hydrochloric acid : this is pre- 

 pared by dissolving carbolic acid in warm hydrochloric 

 acid, adding, whilst the mixture is cooling, sufficient 

 hydrochloric acid to dissolve any precipitate that may 

 be formed. Lignified cells, treated with this mixture 

 and exposed to sunlight, assume a bright green 

 colour in consequence of the presence of coniferin. 



Aniline sulphate and chloride. These salts are 

 also used as tests for lignin in cell-walls ; the chloride is 

 preferable. They may be used in solution either in 

 water or alcohol, but the alcoholic solution gives the 

 best results. The section is first treated with the solu- 

 tion and then with sulphuric or hydrochloric acid re- 

 spectively, or better, the solution may be kept slightly 

 acidulated by one or other ot these acids : the lignified 

 cell- walls assume a bright yellow colour. 



VI. Mixtures. 



Schulze's Solution 1 (Chlor. Zinc lod.). Used 

 as a test for cellulose ; cellulose cell-walls turn blue 

 when treated with this mixture ; corky and lignified 

 cell- walls turn yellow, protoplasm brown, and starch blue. 



1 Since there has been some uncertainty as to the exact name of 

 the botanist who introduced these reagents, it may be here stated that 

 they were first used by Professor Franz Sclmlze, of Rostock. See Flora, 

 1850, p. 643. 



