646 SOME SPECIAL METHODS 



coloration. Crocein and nigrosin stain lignified and suberised 

 walls, but not the pectic substances. Crocein, naphthol black, 

 orseille red, Congo red and azo-blue stain pure cellulose but not 

 pectic substances. 



See also Mehta, Biochem. Journ., xix, 1925, p. 979 and section 

 on Staining. 



1276. Mucilage and mucilaginous walls swell in water, are 

 insoluble in alcohol and ether and are readily stained with methy- 

 len blue and gentian violet. Slimes may sometimes be differen- 

 tiated by colour reactions, though they are often mixtures. See, 

 especially, Mangin, Bull. Soc. Bot. France, xli, 1894, p. 40. 



1277. Cellulose derivatives hardly react to iodine. They stain 

 with alkaline solution of Congo red. 



1278. Pectose derivatives stain brown with lead acetate and 

 with alum. They are stainable with neutral solutions of haemato- 

 xylin, methylen blue, neutral red and ruthenium red. 



1279. Callose derivatives, which are readily soluble in dilute 

 NaOH or KOH, stain with an acid solution of anilin blue. 



1280. Gums swell and dissolve in water, are soluble in alcohol 

 and are stained red with an ammoniacal solution of ruthenium 

 red. Many stain well with corallin soda, anilin blue and anilin 

 violet. 



1281. Suberin and cutin are unaffected by eau de Javelle and 

 are comparatively insoluble in HgSOj and in chromic acid. Suberin 

 becomes invisible in the latter reagent owing to its dark colour, but 

 requires several days for solution. Both give a yellow-brown 

 colour with iodine followed by sulphuric acid. Phloroglucin, 

 followed by HCl, produces a deep pink colour. Concentrated 

 aqueous KOH gives a bright reddish-yellow colour with suberin, 

 and a bright yellow colour with cutin ; the colours are somewhat 

 intensified on warming (von Hohnel, Sitzungsher. Ak. Wiss. Wien., 

 Ixxvi, 1877, p. 507). They turn yellow-brown with chlor-zinc- 

 iodide, especially in sections treated with eau de Javelle and 

 washed with 1 per cent. HCl (von Hohnel, 1. c). They are 

 stained red by alcoholic solutions of alkanin, Sudan III, and 

 Scharlach R., and are also stained by chlorophyll (see 

 Zimmermann, Zeit. wiss. Mik. mik. Tech., ix, 1892, p. 58 ; Soar, 

 New Phyt., xxi, 1922, p. 269). Neutral violet (1 : 10,000 aqueous 

 solution slightly acidified) is said to stain suberin violet, but not 

 cutin. 



They are usually stained similarly to lignin by ordinary histo- 

 logical methods. Stains which, in addition to colouring lignified 

 walls and cork sharply differentiate cutinised cellulose, are in 

 order of merit : Magdala red (genuine), methyl green, solid green, 

 malachite green, gentian violet and fuchsin. Less useful are : 

 safranin, methyl blue, neutral red, erythrosin and eosin. The 

 stains are best used in dilute aqueous solution. To correct over- 



