SOME SPECIAL METHODS 645 



A dull brown colour is produced by KOH, and a deep brown 

 colour by chlor-zinc-iodide. 



Most lignin reactions appear to be due to bodies of an aldehyde 

 nature (probably coniferyl aldehyde). For the lignin complex 

 itself, Cross and Bevan's chlorine — sodium sulphite reaction 

 (J. Chem. Soc, Iv, 1889, p. 199) seems most reliable (see Schorger, 

 J. Ind. Eng. Chem., xv, 1923, p. 812). Exposure to moist chlorine 

 gas or bromine or treatment with chlorine water produces a yellow 

 colour, changed to red on the addition of sodium sulphite. In the 

 Maule reaction {Funfstuk's Beitr. wiss. Bot., vi, 1900, p. 166) 

 material is first treated with oxidising agents. For example, 

 treat with 1 per cent, potassium permanganate five minutes, then 

 with HCl and wash with water and add ammonia. A bright red 

 coloration results ; the wood of Gymnosperms, however, usually 

 gives a brownish-grey. 



For a summary of numerous other reactions see van Wisselingh 

 and the references there quoted. See also Crocker, J. Ind. Eng. 

 Chem., xiii, 1921, p. 625 ; Abrams, J. Ind. Eng. Chem., xiii, 1921, 

 p. 786. 



1275 bis. Pectic Substances occur principally as the calcium salt 

 of pectin in the cell-walls of higher plants, especially in the middle 

 lamella. They are soluble in macerating liquids and (especially 

 in fruits) in boiling water and very dilute acids. They are soluble 

 also in ammonium oxalate and in HCl followed by KOH ; the 

 latter method requires careful management. 



Neutral violet stains pectin a brown-red colour. 



Ruthenium red (see Mangin, Bull. Soc. Bot. France, xli, 1894, 

 p. 40) does not stain pure cellulose and possesses more affinity for 

 pectic substances than any other stain used in botanical technique. 

 It is best used in neutral or slightly ammoniacal solution. 

 Ruthenium red, however, also stains gums, mucilages (Mangin ; 

 TuNMAN, PJlanzenmikrochemie, 1913), fatty acids (Tupper Cary 

 and Priestley, Proc. Roy. Soc. Lond., cxv, 1923, p. 109), gelose 

 (Tunman), etc. 



Treatment with Schweizer's reagent by the method of Fremy 

 {Compt. rend., Ixxxiii, 1876, p. 1136) removes the cellulose and 

 leaves the pectic substance of the cell-wall as an insoluble frame- 

 work, which can be stained with ruthenium red (Carre and 

 HoRNE, Ann. Bot., xli, 1927, p. 193). 



See also Howe, Bot. Gaz., Ixxii, 1921, p. 313. 



Affinity of Cellulose, Lignin and Pectic Substances for Stains. 

 Mangin {Compt. rend., cix, 1889, p. 579 ; ex, 1890, pp. 295 and 644) 

 finds that pectic substances, lignified and suberised walls stain 

 with methylen blue, Bismark brown and fuchsin, while pure 

 cellulose does not. If such stained sections are treated with 

 alcohol, glycerin or dilute acids the pectic substances are 

 decolourised rapidly, whereas the lignin and suberin retain their 



