DETECTION OF SUBERIN, ETC. 145 



4. Calcium chloride iodine solution turns lignin yellow to 

 yellow-brown. 



5. Insoluble in cuprammonia. 



6. Aniline sulphate or aniline chloride in aqueous solution 

 and acidified with the appropriate acid turns lignified walls a 

 bright yellow. 



7. If the sections be soaked for about a minute in an 

 alcoholic solution of phloroglucin (or resorcin, hydroquinone, 

 pyrogallol, or pyrrole) and then mounted in a drop of strong 

 hydrochloric acid, the lignified walls are turned a bright red. 



8. A concentrated solution of thallin sulphate in 50 per 

 cent alcohol gives a yellow to orange-yellow coloration. 



The sections should be treated first with alcohol, and the 

 thallin sulphate solution should be freshly prepared. 



The colour-reactions obtained by the use of aniline sul- 

 phate, thallin sulphate, phloroglucin and the other reagents 

 mentioned in paragraph 7, are due to the presence of the 

 furfurol complex in the lignin ; any substance in the plant 

 which contains this complex, e.g. coniferin, will give similar 

 reactions. 



9. If lignified tissues be treated with chlorine water and 

 then with sodium sulphide, a deep magenta colour is produced. 



10. Lignocelluloses induce the formation of Prussian blue 

 in the greenish-red solution produced by mixing ferric chlo- 

 ride with potassium ferricyanide. 



(b) Suberin and Cutin. 



1. With chlorzinc iodide, and also with iodine and sul- 

 phuric acid, a brown or yellow colour is given. 



2. Suberized and cuticularized walls are insoluble in 

 cuprammonia and concentrated sulphuric acid. 



3. Suberized walls are coloured yellow with strong potash 

 solution ; on heating the colour deepens, and on boiling 

 yellow oily drops exude from the membranes. 



4. Suberized walls are the most resistant of membranes to 

 Schultze's macerating mixture ; but on boiling, oily drops of 

 eerie acid are formed which are insoluble in carbon bisulphide 

 but soluble in ether, benzol, and hot alcohol. 



5. Suberized and cuticularized walls are stained green by 

 the action of alcoholic solutions of chlorophyll. A strong 



10 



