80 The Microscope. 



they remain too long in the dye the red will drive out the green. 

 Transfer to at least two ounces of water and soak at least three 

 hours to take out the alum, or it will crystallize in the slide. But 

 the ferns seem to differ from each other chemically, and it may be 

 found necessary to vary the formula in some cases to avoid the sec- 

 ondary tint. It will also be found difficult to stain the very thick- 

 leaved ferns by this process without making them too opaque, and 

 for them the next process will be found more satisfactory. 



For thick-leaved ferns, or for showing the libro-vascular system 

 and sporangia: 



To forty drops of borax carmine add one drop of methyl green. 

 This requires more time in the dye; indeed, there is little danger of 

 overstaining, for it is hard getting the borax carmine into the sub- 

 stance of the leaf, and at best the color will be very delicate, but if 

 successful the result will be very satisfactory. Soak as before, or 

 the carmine adhering to the surface of the leaf will make trouble in 

 the slide. A saturated solution of acetate of alumina used as a 

 mordant after soaking will brighten the color a trifle. 



MOUNTING. 



The best medium for mounting ferns is glycerine jelly made 

 after Kaiser's formula, with additional gelatin to give it hardness. 

 Balsam makes a ghostly slide showing little of details, and glycerine 

 requires a very deep cell and is not as satisfactory in any respect; 

 but glycerine jelly is hardest of all to manage, so far as my expe- 

 rience goes, except by the following method. 



First transfer to C. P. glycerine and alcohol, half and half, 

 filtered, and do not let the alcohol dry ofP in making the change; if 

 you do, the air will get into the leaf and ruin it. Next heat the 

 glycerine jelly in a water bath, and keep it hot while using, to pre- 

 vent trouble from air bubbles. With a glass rod place a few drops 

 on the slide, with or withovit a cell, — a cell makes the better finish. 

 Place the ferns in the glycerine jelly, add a few drops, and pour off 

 to get rid of the alcohol and glycerine, replace what is poured off 

 and examine with dissecting microscope for air bubbles, which must 

 be removed for they will never leave after the cover is on. Breathe 

 on the cover and apply a drop or two of hot glycerine jelly, then 

 breathe on the slide and apply the cover. 



Another way is to let the glycerine jelly harden on the slide 

 with the fern in it, and at your leisure apply a layer of hot glycerine 



