76 Botanical Microtechnique 



The following version recognizes that it is cheaper to rinse out 

 stains and mordants in water than in alcohol, and also prolongs the 

 usefulness of the dehydrating series. The stain is a 1/4 to V^% 

 aqueous solution of crystal (gentian) ^ iolet. Ihc mordant is aqueous 

 IKI (Chajx 9) . The picric acid solution is a saturated solution in 

 50% alcohol. De-waxing and running down to water are carried 

 out in Coplin jars. However, the slides nuist be carried one by one 

 through the dehydrating series, which must not contain other stains 

 as contaminants. Therefore, a sjjccial dehydrating set shoidd be 

 maintained for the violet process, preferably in wide-mouth screw- 

 capped jars. 



Differentiation is accomplished in the alcohol dehydrating series. 

 The slide shoidd be agitated in the fluids with forceps. Observe 

 closely in the 95% alcohol, and when visible color no longer comes 

 out of the sections, move rapidly through anhydrous alcohol. Differ- 

 entiation shoidd be complete when the alcohol-xylene-cedar oil clear- 

 ing solution is reached. The function of the oil is to retard evapora- 

 tion to j^ermit examination. If the cytoj^lasm is too blue, back down 

 to 95% alcohol. If the blue has been lost from the chromosomes, 

 carry back to water and IKI and restain. 



The Tannic Acid-Ferric Chloride Stain (Foster) 



This stain is used lor meristematic tissues, in which it stains the 

 thin cell walls. Because of the simplicity of the schedule, no chart 

 is necessary. The reagents thai bring about the staining are as follows: 



1. Tannic add. 1% aqueous, \vitli \% sodium benzoatc as a preservative. 



2. Ferric (hloiidc. ,8% a(|ucous soluiion. 



The ])rocediU"e Irom \vatei' is as l()ll()^\•s: 



1 . lannic ac id 10 min. 



2. Wash tliorout;lily in water. 



3. Ferric diloiidc. 2-.^ niin. 



4. Wash ill wati'i, and cxaniiiif \\illi iiiic rose ope. 



Re]>eat stejjs 1 to 1 iiuhisi\c' until the (ell walls are sharply 

 outlined. Xiulci nia\ be stained in safranin il desired, using atjueous 

 safranin, or safranin in M)' i alcohol. 



Variations of the fundamental method are described by Northen 

 (19,Sr)) . riiis stain is likely to undergo further modification and will 

 probabK become one of our most useliil histological stains. 



I he loic'going outline ol the elements ol staining jMoccsses is 

 likely to be ade(|uate for liie a\erage needs of sludenis and teachers 



