676 PLANT CHROMOSOMES 



is suitable for smears : 1 per cent, chromic acid, 60 c.c. ; 2 per 

 cent, osmic acid, 20 c.c. ; 10 per cent, acetic acid, 25 c.c. 



Rancken {Acta Agralia Fennica, xxix, 1934, p. 9) uses 30 c.c. 

 of 5 per cent, acetic acid in this mixture for fixing root-tips. 



Taylor {Bot. Gaz., Ixxviii, 1924, p. 236) adds maltose according 

 to the following formula, to assist spreading of the chromosomes 

 and to prevent clumping : 10 per cent, chromic acid, 0-2 c.c. ; 

 10 per cent, acetic acid, 2-0 c.c. ; 2 per cent, osmic acid in 2 per 

 cent, chromic acid, 1-5 c.c. ; water, 8-3 c.c. ; maltose, 0-15 grm. 



Catcheside's {Ann. Bot., xlviii, 1934, p. 601) modification is 

 useful on smears of pollen mother-cells with small chromosomes. 

 10 per cent, chromic acid, 3 c.c. ; 10 per cent, acetic acid, 2 c.c. ; 

 2 per cent, osmic acid, 1-5 c.c. ; maltose, 0-2 grm. ; water, 10 c.c. 



La Cour's {Nature, cxxiv, 1929, p. 127) two formulae give 

 chromosomes well spread and constrictions well marked. 2B is 

 1 per cent, chromic acid, 90, c.c. ; potassium bichromate, 1 grm. ; 

 sodium sulphate, 0-5 grm. ; urea, 1 grm. ; 5 per cent, acetic acid, 

 10 c.c. ; 2 per cent, osmic acid, 15 c.c, ; distilled water, 45 c.c. 



La Cour {J. Roy. Micr. Soc, li, 1931, p. 119) gives two further 

 formulae ; 2BE is best for root-tips and smears, 2 BD is useful 

 after Carnoy by Kihara's method, 2BE : 1 per cent, chromic 

 acid, 90 c.c. ; potassium bichromate, 1 grm. ; saponine, 0-05 grm. ; 

 5 per cent, acetic acid, 10 c.c. ; 2 per cent, osmic acid, 15 c.c. ; 

 distilled water, 45 c.c. 2 BD. : 1 per cent, chromic acid, 100 c.c. ; 

 1 per cent, potassium bichromate, 100 c.c. ; saponine, 0-1 grm. ; 

 5 per cent, acetic acid, 30 c.c. ; 2 per cent, osmic acid, 30 c.c. 



Bi^LAR's modified Flemming-Benda (Meth. Wiss. Biol, i, 1929, 

 p. 638) is satisfactory with smears : 2 per cent, osmic acid, 4 c.c. ; 

 1 per cent, chromic acid, 15 c.c. ; acetic acid, 2 to 3 drops. 



Smith (J. Genet., xlix, 1935, p. 119) gives two modifications for 

 pollen mother-cells. Si for early prophase and S2 for diakinesis and 

 metaphase stages. 



Various substitutes for osmium tetroxide have been employed. 



Carpenter and Nebel {Science, Ixxiv, 1931, p. 154) recommend 

 ruthenium tetroxide. Prepare the stock solution by breaking a 

 1 grm. ampoule under 100 c.c. of chlorine water. For use, dilute 

 about twenty times with distilled water or a 0-25 to 1 per cent, 

 solution of formic or acetic acid. The correct concentration is 

 that which gives a medium grey colour when a drop is placed on 

 filter paper. 



