60 METHODS IN PLANT HISTOLOGY 



system of living plants. It does not diffuse during dehydration or 

 clearing. Detailed directions are given on page 151. 



Dissolve 0.5 g. basic fuchsin in 20 c.c. of 95 per cent alcohol and 

 dilute with 1,000 c.c. of tap water. A smaller quantity can be made by 

 dissolving 50 mg. in 2 c.c. of 95 per cent alcohol and diluting with 100 

 c.c. of tap water. 



Congo red. — This is an acid stain resembling acid fuchsin. For cy- 

 tological work use a | per cent aqueous solution; for anatomical work 

 use a saturated solution. It is a good stain to use after malachite 

 green or anilin blue. Transfer to the Congo red from water, stain 15 

 minutes, wash in water, transfer — for wood sections — to 85 per cent 

 alcohol, and wash until the green or blue color of the previous stain 

 begins to show through the red. Then treat quickly with absolute al- 

 cohol, clear in xylol, and mount in balsam. 



Eosin. — This has long been a favorite stain, but for most purposes 

 it has been replaced by similar stains giving better differentiation. 

 The dry stain is made in two forms, one for aqueous and the other for 

 alcoholic solution. Each should be used with its intended solvent. 

 Make a 1 per cent solution in alcohol or water. It is worth mentioning 

 that the aqueous solution is an excellent red ink. 



For material to be mounted whole in glycerin, glycerin jelly, or 

 Venetian turpentine, stain overnight or, better, 24 hours; pour off the 

 stain, which may be used repeatedly; treat, without washing in water, 

 with a 2 per cent aqueous solution of acetic acid for 5 or 10 minutes, 

 changing 2 or 3 times; transfer to 10 per cent glycerin without washing 

 in water, since the stain will be brighter if the whole solution is slightly 

 acid. When the glycerin becomes thick, mount in glycerin jelly. If the 

 Venetian turpentine method is to be used, wash the glycerin out in 

 alcohol shghtly acidulated with acetic acid (a couple of drops of acetic 

 acid to 50 c.c. of alcohol), and do not drain off the last alcohol too com- 

 pletely before transferring to the 10 per cent Venetian turpentine. 

 According to Lee, the glycerin should be slightly alkaline. The alka- 

 linity can be brought about by adding half a gram of common salt to 

 100 c.c. of the 10 per cent glycerin. We have found that eosin keeps 

 better when the media are slightly acid. 



For staining paraffin sections, the alcoholic solution is better and 

 the time may not be more than a few minutes, especially if the eosin is 

 being used as a contrast stain. 



We have found the Eosin Y, of Coleman and Bell, very satisfac- 



