INTERCELLULAR SUBSTANCE. 77 



sulphate, the addition of warm concentrated potas- 

 sic hydrate often colors them brown. An aqueous 

 solution of sulphate of aniline (naphthalidin or 

 toluidin), followed by saturation with dilute sul- 

 phuric acid, colors them a beautiful yellow (Wies- 

 ner's reaction). Frequently this reaction is ob- 

 tained without the use of any acid. All membranes 

 which contain lignin assumes an intense and very 

 beautiful rose color, due to the presence of vanillin, 

 when treated with hydrochloric acid and phloro- 

 glucin. The same reaction is given by this acid in 

 combination with an extract of cherrywood (Xylo- 

 filin), but the color is more violet. On the other 

 hand, a bluish-green color appears after the succes- 

 sive action of hydrochloric acid and phenol. 



All aniline colors are taken up with avidity by 

 lignified membranes. Indol gives them an in- 

 tense red color. Grenadier's alum carmine does 

 not color them. A weak aqueous solution of eosin 

 produces no color after short action, though the 

 same is true of pure cellulose. Lignified mem- 

 branes lose the so-called incrusting substances by 

 being heated with alkalies, concentrated nitric acid, 

 or the Schultze maceration fluid, after which the 

 cellulose reaction can be produced by the proper 

 reagents. 



INTERCELLULAR SUBSTANCE (''Middle Lamella"). 



Insoluble in concentrated sulphuric acid, cu- 

 prammonia, and dilute chromic acid ; soluble with 



