STAIN TECHNIQUE 29 



In the contrast staining of plant tissues mordant the material 

 for 15 minutes in J per cent potassium dichromate, rinse in dis- 

 tilled water, use Orange G overnight, rinse again with distilled 

 water, and follow with : ( 1 ) one minute in Methyl Violet, C. I. No. 

 680, (2) five minutes in Niagara Sky Blue, C. I. No. 520, or (3) 

 five minutes in New Methylene Blue, C. I. No. 927. 



28. Ponceau G, 2G, Scarlet 2G is an acid dye, light 3 to 4 ; J 

 gram in 100 ml. of distilled water and 1 ml. of 1 per cent sulfuric 

 acid. Many tissues are stained fuchsia. Materials previously 

 treated with potassium dichromate are scarlet and more fast to 

 washing. One of the "poppy" dyes, it is similar to Ponceau 3R, C. I. 

 No. 80, and Crocein Scarlet MOO, C. I. No. 252. On animal tissues 

 use Ponceau G in the same manner as described in the technique for 

 Crocein Scarlet MOO. 



On plant tissues use the stain for 12 to 24 hours and follow 

 with: (1) Victoria Blue B, C. I. No. 729, five minutes for reddish 

 brown and blue, (2) Methyl Violet, C. I. No. 680, one minute, or 

 (3) Niagara Sky Blue, C. I. No. 520, five minutes for reddish 

 brown and blue. 



29. Chromotrope 2R is an acid dye, light 4. There are many 

 acid dyes of a nondescript fuchsia; this one is very fugitive to 

 light. As successive azo dyes are considered notice the progressive 

 increase of color intensity. 



30. Azofuchsine, Acid Azofuchsine is an acid dye, light 3. 

 The bright fuchsia obtained on plant tissues is changed to bordeaux 

 with either a mordant or an after-treatment of potassium 

 dichromate. 



31. Pontacyl Carmine 2G (Du Pont) is an acid dye, light 3. 

 This fuchsia pigment is more intense than the color obtained with 

 Azofuchsine. After a potassium dichromate mordant, the color 

 changes to bordeaux. Fungous mycelia treated with a mordant 

 remain light fuchsia. 



36. Alizarin Yellow G, and 40. Alizarin Yellow R are mor- 

 dant dyes, light 5. The color on paraffin sections is fugitive. The 

 alcoholic solution of the dye stains blue-green algae a brilliant yel- 



