GENERAL TECHNIQUES FOR CLASSES OF PLANTS 715 



anthers with 95 per cent, alcohol, followed by a large drop of dis- 

 tilled water. Heat slide until water boils, open anthers and press 

 out the pollen. Stain and pass into glycerin or glycerin jelly. 

 To mount dry or shrunken material, stain in a drop of anilin oil, 

 moderately tinted with gentian violet. Heat over a flame until 

 the oil steams ; if necessary continue for several minutes to secure 

 a good stain. Dry off part of the oil and add a drop of balsam. 



Margolexa {Stain Tech., ix, 1934, p. 71) fixes in Bouin and stains 

 in 0-5 per cent, aqueous solution of Bismarck brown. Rinse in 

 water, dehydrate with 95 per cent, absolute alcohols. Counter- 

 stain and differentiate with about 0-3 per cent, fast green FCF in 

 clove oil. Clear in xylol. Exine green, intine brown, nuclei 

 brown. Ferguson and Coolidge {Amer. J. Bot., xix, 1932, 

 p. 644) consider that descriptions of pollen grains observed in 

 aqueous media are of doubtful value. They find that grains of 

 Petunia do not change appreciably in size and shape when passed 

 directly from dry air to xylol balsam, where they remain per- 

 manently unchanged. 



Chamberlain recommends that loose pollen of anemophilous 

 plants should be soaked a few minutes (fifteen to twenty) in water 

 before fixation in bulk and handling like minute organisms. 



1408. Pollen counts to determine percentages of normal and 

 abnormal or empty grains are made from covered mounts in a 

 drop of iodine solution or in 45 per cent, acetic acid lightly 

 coloured with iodine. Care should be taken to sample the prepara- 

 tion thoroughly as the smaller and empty shrivelled grains tend 

 to collect at the edges of the coverslip. Make measurements 

 soon after mounting the pollen as they will swell (and burst) or 

 sometimes shrink quite rapidly, often in thirty to sixty minutes. 



See Blakeslee and Cartledge, Proc. Nat. Acad. Sci., U.S.A., 

 xii, 1926, p. 315. 



1409. Pollen Germination. Most pollens rapidly lose their 

 vitality, so that tests should not be delayed. Some grow well on 

 slides kept in a damp chamber. Others require water ; allow 

 the drop to spread thinly on a clean slide so that oxygen is readily 

 available. Most will germinate in a solution of sucrose, the 

 optimum concentration of which varies with the species, and 

 from year to year, over a wide range. Doroshenko {Bull. Appl. 

 Bot., Genet, and Plant-Breed., xviii, 1928, p. 217) gives a table for 

 over 500 spp., as to the optimum conditions for the germination 

 of their pollen in vitro, for its storage and for its longevity.. 



Trankowsky's Method {Planta, xii, 1930, p. 1). Slides are 

 spread with a thin coating of agar (1 to 2 per cent.) containing 

 sugar in suitable concentration, dusted with pollen and placed in 

 a moist chamber. After germination the slide may be fixed, 

 stained and moimted in balsam. 



See also Poddubnaja-Arnoldi, Planta, xix, 1933, p. 299. 



