GENERAL STAINING 651 



For the effect of pH on differential staining, see Naylor, 

 Amer. Journ. Bot., xiii, 1926, p. 265. 



Material mounted in glycerin jelly may be stained by adding 

 small amounts of stain to the jelly. 



Pre-staining before sectioning is little used ; see Otis, Science, 

 Ixvi, 1927, p. 196 (alcohol-xylol-safranin method). 



McLean (New Phyt., xxxiii, 1934, p. 316) stains material 

 with the free aeids of erythrosin and eosin dissolved in xylol. 

 Dissolve 1 grm. of stain in 100 c.c. water and add 10 per cent. 

 HCl (s.g. 1-16), 3-5 c.c. for the erythrosin and 2-5 c.c. for the 

 eosin. Allow the precipitate to settle and after twenty -four hours 

 pipette off the clear liquid. Add 200 c.c. xylol and shake very 

 gently or stir with a glass rod ; avoid an emulsion. Separate 

 off the (nearly colourless) xylol extract. Stain with it after 

 clearing in xylol. The free base of methylen blue (Nile blue 

 is better) can be used similarly. Precipitate it by adding 2-5 c.c. 

 10 per cent. NaOH for each gram of the dye. The two xylol 

 stains can be used successively, but not mixed. 



See Stevens and Hawkins, Journ. Agr. Res., vi, 1916, p. 362. 



Single stains are usually preferable for apical cells, young 

 antheridia, archegonia and other relatively undifferentiated 

 structures, if the preparations are for anatomical study. In such 

 cases, stains which deeply colour the cell-walls without obscuring 

 them by also colouring starch, plastids and other cell contents, 

 should be used. Further, it is better not to counterstain the 

 cytoplasm in these cases, as the dense cytoplasm often takes a 

 heavy stain and obscures the walls. 



Combination stains have a wide application for differentiation 

 between elements that are lignified or suberised and those that 

 are not. It is usually best to combine a basic with an acid stain, 

 the former for lignified and suberised, the latter for cellulose walls. 

 A great number of stain combinations have been employed ; some 

 of the more widely used and successful ones are described below. 



1288. Staining of Ribbons of Sections without Removal of 

 Paraffin. Stretch ribbons as usual and float them upon the 

 surface of the stains and then distilled water. Float them into 

 place upon the surface of an albumenised slide, dry, clear and 

 mount. Sections of the same tissues may be stained by different 

 methods and mounted side by side for comparison. The removal 

 of the paraffin is necessary only in case a very narrow diaphragm 

 opening is used. 



Forceps with broad, flat, blunt ends about 2 to 4 mm. wide 

 are useful for picking up the ribbons. The end of the ribbon 

 may be gripped with such an instrument and the whole ribbon 

 easily lifted by a gentle pulling motion. 



See McFakland, Science, Ivi, 1922, p. 43 ; de Fraine, New 

 Phyt., xii, 1913, p. 123. 



