54 Methods in Plant Histology 



Eosin. This has long been a favorite stain, but for most pur- 

 poses it has been replaced by similar stains giving better differentia- 

 tion. 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. 



For algae or fungi to be mounted in glycerin use the aqueous 

 solution and stain for several hours ; treat with 1 per cent acetic acid 

 for several seconds, and then wash the acid out thoroughly in water. 

 Place in 10 per cent glycerin, and allow the glycerin to concentrate. 

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

 alkalinity 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 well when the glycerin is acidulated with about 1 c.c. glacial 

 acetic acid to 100 c.c. of 10 per cent glycerin. 



For staining paraffin sections, the alcoholic solution is better. 

 One or two minutes is usually sufficient, and it is not necessary to 

 use acid. 



Haematoxylin and eosin and methyl blue and eosin are good 

 combinations. The eosin should follow the other stain. 



Erythrosin.--This is really an eosin, but there is some difference 

 in the method of manufacturing. It is a more precise and a more 

 transparent stain than eosin and is to be preferred for nearly all 

 staining of paraffin sections. Make a 1 per cent solution in distilled 

 water or in 70 per cent alcohol. It gives good results when made up 

 according to the general formula. 



Erythrosin stains rapidly, 30 seconds to 3 minutes being sufficient. 

 When used in combination with other stains, erythrosin should come 

 last. 



Magdala Red. At least two Magdala reds are sold by dealers, 

 one the echt (genuine) Magdala red, and the other simply Magdala 

 red. The latter is much cheaper and, in our experience, much 

 superior to the echt stain. The directions apply to the cheaper stain. 



For staining algae which are to be mounted in Venetian tur- 

 pentine, use a 1 per cent solution in 85 or 95 per cent alcohol. Dilute 

 the stain about one-half with 95 per cent alcohol and allow it to act 

 for 6 to 8, or even 24, hours. Rinse in 95 and 100 per cent alcohol 



