26 METHODS IN PLANT HISTOLOGY 



h) Weak chromo-acetic solution (Shaffner's formula). — 



Chromic acid . 3 g. 



Acetic acid 0.7 c.c. 



Water 99.0 c.c. 



This has also been used in embryological work. It causes little or no 

 plasmolysis. Difficult material, like Aster heads and ripe Capsella 

 pods, cuts more readily after this reagent than after the stronger solu- 

 tions. 



c) Strong chromo-acetic solution. — 



Chromic acid 1 g- 



Glacial acetic acid 3 c.c. 



Water 100 c.c. 



For fern prothallia, most liverworts, moss capsules before they have 

 begun to get reddish or brownish, and most filamentous algae and 

 fungi, this is a good fixing agent. 



d) Licent's formula. — 



One per cent chromic acid 80 c.c. 



Glacial acetic acid 5 c.c. 



Formalin 15 c.c. 



This formula has been recommended for coenocytic algae and fungi 

 and for embryo sacs. 



The most famous and, up to the present time, the most satisfactory 

 of all the chromic mixtures, are the Flemming solutions or modifica- 

 tions of them. In his work on mitosis and upon the structure of proto- 

 plasm he used two solutions, commonly called the stronger and weaker 

 solutions, which contained osmic acid in addition to the chromic and 

 acetic acids. Various proportions of the three ingredients have been 

 used by various investigators. 



While the chromic and acetic acids may be made up in a stock solu- 

 tion, it should be remembered that the acetic acid will evaporate un- 

 less kept in a very tightly stoppered bottle. The osmic acid should be 

 kept in a tightly stoppered bottle, always using a glass stopper, and 

 the bottle should be completely covered with black paper. The 

 osmic acid must not he added to the other two ingredients until you are 

 ready to drop the material into the fixing agent. 



