642 SOME SPECIAL METHODS 



tube heated externally by a coil of resistance wire ; a rheostat 

 in the circuit controls the temperature. The material is heated 

 gently until carbonised and then to a dull red heat for half to one 

 and a half hours. Sections may also be heated on a platinum 

 plate over a Bunsen burner until they are reduced to a white ash. 

 The ash is then transferred without alteration to a slide coated 

 with collodion. The sticky collodion takes up the crystals, which 

 sink into the collodion if the slide is held inverted over vapour of 

 alcohol ether. On drying, the thin film of collodion, with the 

 imbedded crystals, may be removed from the slide with a razor 

 blade and mounted in balsam or an aqueous medium. Ohara 

 transfers the ash froiu the platinum plate to anilin oil, in which it 

 is immediately ready for study. 



See MoLiscH {Sitzungsber. Akad. Wiss. Wein [Maih.-Nat. KL), 

 Abt. I, cxxix, 1920, p. 261) ; Ohara {Akad. Wiss. Wein. Math.- 

 Nat. K. Denkschr., c, 1926, p. 301) ; Kisser (Abderhalden Handb. 

 Biol. Arbeits7nethoden Abt., xi, Teil, iv, 1931, p. 193) ; Policard 

 {Protoplasma, vii, 1929, p. 464) ; Policard and Okkels {Anal. 

 Bee, xliv, 1930, p. 349) ; Scott {Protoplasma, xx, 1933, p. 133) 

 (critical review). 



1270. Growth of Cell-wall is studied by precipitating a stain in 

 the wall. Nell {Wurzburger Habilitationsschrifl Abhandl. 

 Senckenburg tiat. Ges., xv, 1887, p. 101) used a precipitate of 

 Berlin blue (potassium ferrocyanide and ferric chloride) or of 

 Turnbull's blue (potassium ferricyanide and ferrous lactate) in the 

 walls of marine algae such as Caulerpa. Immerse the alga, for a 

 few seconds, in a mixture of 1 part sea-water, 2 parts fresh water 

 and sufficient potassium ferrocyanide to give the solution the 

 density of sea-water. Rinse rapidly in sea-water and immerse 

 half to two seconds in a mixture of 2 parts sea-water, 1 part fresh 

 water and a few drops of ferric chloride. Repetition intensifies 

 the colour, which, however, is gradually destroyed afterwards. 



Zacharias {Flora, 1891, p. 467) and Klebs {Untersuch. bot. Inst. 

 Tubingen, ii, p. 489) have used Congo red. 



For the daily growth rings in cotton hairs. Balls {Proc. Roy. 

 Soc. Lond., B, xc, 1919, p. 542) wells them to five to ten times their 

 normal size by treatment with NaOH and carbon bisulphide. 



1271. Finer Structure of Cell-walls. See especially Correns 

 {Pringsheim's Jahrb. wiss. Bot., xxiii, p. 254). The fine sculp- 

 turing may be observed in media of low refractive index, e.g. 

 methyl alcohol (/x = 1-321). Differentiations due to unequal 

 water-content require drying at 100° C, as absolute alcohol, and 

 other dehydrants do not give positive results. Afterwards 

 impregnate the wall with Berlin blue or silver. For the latter, 

 place well-dried objects in 2 to 5 per cent, aqueous silver nitrate, 

 dry superficially but do not wash, and then place in 0-75 per cent, 

 aqueous NaCl. Reduce the AgCl thus precipitated by exposure 



