514 PRACTICAL BOTANY 



agent, before mounting in Canada balsam. A small quantity 

 is to be added to glycerine jelly to prevent the growth of 

 Fungi. 



Phloroglucin. Dissolve some phloroglucin in methylated 

 spirit, and gradually add strong hydrochloric acid till precipitation 

 begins ; the liquid is then ready for use : in sections treated with 

 it lignified walls assume a bright red colour. 



Picric Acid. A saturated solution in water is very generally 

 used for fixing the protoplasm of the cell as nearly as possible in 

 the form which it held during life (p. 5). It is, however, objection- 

 able, owing to the difficulty in completely washing it out from the 

 specimens before hardening in alcohol, and in most cases treat- 

 ment at once with absolute alcohol is to be preferred. In some 

 cases, such as delicate Algae, it is well to dilute the saturated 

 solution with an equal volume of water. 



Picro-carmine (or ammoniun picro-carminate) is prepared 

 by adding a strong ammoniacal solution of carmine to a quantity 

 of concentrated solution of picric acid in water, until a pre- 

 cipitate begins to be formed ; it is then evaporated to about 

 one-fifth of its bulk, filtered, and the filtrate is evaporated to 

 dryness. The crystalline residue is dissolved in water so as to 

 make a 5 per cent, solution, and this may be diluted as occasion 

 requires. 



Another method (Gage) is to dissolve a quantity of picric acid 

 in 100 parts of water, and an equal quantity of carmine in 50 

 parts of solution of ammonia ; these are then mixed, filtered, 

 evaporated to dryness, and the residue dissolved in 100 parts 

 of water. 



Picro-carmine is used especially for staining nuclei, the staining 

 being more uniform than when carmine alone is used : it has 

 this further advantage, that a prolonged exposure to it does 

 not produce overstaining, as is the case with the other preparations 

 of carmine. The objects should be previously kept for some time 

 in absolute alcohol. If it be desired to retain the double staining 

 which this reagent produces, the sections must be mounted at 

 once in glycerine ; but if the carmine staining only is required, 

 the sections must be washed in water, which will dissolve out 

 the picric acid. When stained sections are mounted in glycerine, 



