692 PLANT CHROMOSOMES 



than Navashin or 2BE) and stains by the gentian violet-iodine 

 method. Permanent smears showing spiral structure are thus 

 obtainable. 



KuwADA and SakaImura {Protoplasma, i, 1926, p. 239) observed 

 spirals in living pollen mother-cells, injected with carbon dioxide 

 by passing the gas over the material. The ^^H markedly affects 

 the visibility of the spirals. They obtained their best results, 

 using a 0-025 per cent, solution of neutral violet extra in a solu- 

 tion of pH 4*38, making observations on the peripheral cells of 

 the groups. See also Sakamura {Protoplasma, i, 1926, p. 537). 



Nebel {Zeits. Zellf. mikr. Anat., xvi, 1932, p. 251) finds that 



slight desiccation prior to fixation leads to deeply stained spirals. 



With more prolonged treatment the spirals stain less deeply 



and with still longer treatment they disappear. Other pre-treat- 



ment he recommends are 12 per cent, alcohol accompanied by a 



temperature increase (Sharp, Bat. Gaz., Ixxxviii, 1929, p. 349), 



95 per cent, alcohol followed by water, brief treatment with 



N 

 Carnoy before Flemming fixation and — Ringer for twenty 



seconds. He also recommends fixation in a mixture of equal 

 parts each of 1 per cent, uranyl acetate, saturated aqueous 

 mercuric chloride and 50 per cent, formic acid, with the addition 

 of 2 parts of 2-5 per cent, osmic acid. Rinse off the fixative and 

 mount in Linder's medium and seal. Linder's medium is gly- 

 cerin 40 parts, lactic acid 20 parts, phenol 20 parts, water 20 parts ; 

 add a small amount of carmine. 



Cohen (Stain Tech., ix, 1934, p. 101) states that fixation with 

 4 per cent, phosphoric acid in 4 per cent, formaldehyde, followed 

 by the crystal violet-iodine stain, shows details of the internal 

 structure of chromosomes. 



Pre-treatment with various inorganic salts, e.g. uranium nitrate 

 or potassium nitrate, also appears to be effective. 



Preservation of spirals in somatic chromosomes is more diffi- 

 cult, since the material cannot be well fixed by any of the ordinary 

 methods. Try fixation in aqueous Flemming fluids by finely 

 chopping root-tips under the fixative. 



Nebel's method {Cytologia, v, 1934, p. 1) appears to be the 

 most effective. Place root-tips in 0-1 per cent, solution of com- 

 mercial ammonia for five minutes. Transfer to a 0-01 molar 

 solution of thorium nitrate and finally fix twenty-four hours in a 

 mixture of 10 parts of 2-5 per cent, osmic acid in 1 per cent, 

 platinic chloride and 3 parts of 1 per cent, aqueous chromic acid. 



See also Strugger, Planta, Arch. Wiss. Bat., xviii, 1932, p. 561 

 for use of pre-treatments ; Taylor, Proc. Internat. Congr. Plant 

 ScL, Ithaca, N.Y., 1, 1926, p. 265. 



