S02IE SPECIAL METHODS 043 



for several hours to full sunlight. See Alvarado {Bol. R. Soc. 

 Esparwla Hist. Nat., xix, 1919, p. 66 and Trab. Mus. Nacion Cien. 

 Nat. Ser. Bot., No. 13, 1918, p. 9) for an application of the tannin- 

 silver method of Achucarro-Rio Hortega (§ 1094). 



1272. Micellae. For methods of study using polarised light see, 

 for instance. Balls, Proc. Roy. Soc. Lorid., B xcv, p. 72 ; Frey, 

 Jahrb. Wiss. Bot., Ixv, 1926, p. 195 ; Naturzviss., xv, 1927, p. 760 ; 

 Ber. Deut. bot. Ges., xliv, 1926, p. 564 ; Protoplasma, xxxiv, 1928, 

 p. 139. 



Cell-wall Substances : Some Microchemical Tests and Stains. 

 For a general account see vax Wisselingh, Die Zellmembranen, in 

 Linsbauer's Handb. Pjianzenanat., iii, 2, 1925 ; also. Brown, 

 Bull. Torrey Bot. Club, xlvi, 1919, p. 127 ; Haas and Hill, 

 " Chemistry of Plant Products," Longmans, 1928 ; Schorger, 

 " Chemistry of Cellulose and Wood," McGraw-Hill, 1926, and 

 others. 



1273. Cellulose swells and dissolves rapidly in concentrated 

 sulphuric acid. 



A blue colour is obtained by treatment with iodine and strong 

 sulphuric acid (Schleidex, Pogg. Ann., xliii, 1838, p. 391). Soak 

 in a solution of 0-3 grm. iodine and 1-3 grm. Kl in 100 c.c. water, 

 followed by a few drops of 60 to 70 per cent, sulphuric acid. 

 Liffnin turns somewhat more vellow than before. 



It stains blue with chlor-zinc-iodide (see van Wisselingh, 

 Jahrb. Wiss. Bot., xxxi, 1897, p. 624). This reagent is also 

 Jcnown as the Herzberg iodine stain. Prepare as follows : Dis- 

 solve 50 grm. of dry zinc chloride (fused sticks) in 25 c.c. distilled 

 water, adjusting the specific gravity to 1-8, and pour 40 c.c, into a 

 tall cylinder. Dissolve 5-25 grm. KI and 0-25 grm. iodine in 

 12-5 c.c. water and add to the zinc chloride solution. Mix well 

 and place in the dark. After twenty -four hours pipette off the 

 clear portion into a black bottle, and add a leaf of crystalline 

 iodine. The solution deteriorates rather rapidly so where colour 

 differentiations are important do not use longer than two weeks. 



A two-solution method due to Novopokrowsky {Beih. bot. zbl., 

 xxviii, 1912, p. 90) gives uniformly good results. Stain for a few 

 seconds in a 1 : 1 : 100 solution of iodine and potassium iodide in 

 water. Then transfer to a solution of 2 parts zinc chloride in 1 

 part of water, where the section is kept moving until a light blue 

 colour is produced. See also Artschwager, Bot. Gaz., Ixxi, 1921, 

 p. 400 ; and Wightman, Paper, xxxi, 1923, p. 14. 



Mangin {Compt. rend, cxiii, 1891, p. 1069; Bull. Soc. Bot. 

 France, xxxv, 1888, p. 421) found iodine and phosphoric acid 

 colour cellulose blue-violet, while iodine and calcium chloride give 

 a rose or violet colour. Iodine with many other salts (AICI3, 

 CaClg, MnClg, SnClg, Ca(N03)2, and Zn(N03)2) stains cellulose, 

 but ZnClg is most sensitive. 



21—2 



