510 PRACTICAL BOTANY 



parts of 70 per cent, alcohol ; filter, and then add a solution of 

 haematoxylin in absolute alcohol until the liquid has a purple- blue 

 colour ; let it stand in a corked bottle exposed to sunlight for 

 about a month ; it is then fit for use. The liquid is to be diluted 

 as required with alum solution. This preparation is most 

 generally employed, and it may be bought from the dealers ready 

 for use. 



3. Expose a few crystals of hsematoxylin to the action of gaseous 

 ammonia in a watch-glass under a bell-jar : then add water, and 

 a good colouring fluid is obtained. The disadvantage of this is 

 that it has to be freshly prepared every time it is required. 



The alum solutions will stain all parts of the cell, including the 

 cell-wall. Their especial uses are (a) to make the cell- walls more 

 evident when they are naturally transparent and colourless ; 

 (&) to stain the protoplasm, so as to make its intimate structure 

 apparent ; (c) to stain the nucleus, so as to demonstrate its presence 

 and to show up its structure. 



The ammoniacal solution is especially adapted for differentiated 

 staining. If a dilute solution be used, the first thing to become 

 stained is the chromatin of the nucleus, then, after a time, the 

 rest of the nucleus (achromatin), then the protoplasm. The cell- 

 walls do not stain with this fluid, or only slightly. Kleinenberg's 

 hsematoxylin stains in a few minutes, whereas the alum solution 

 is much slower in its action. 



Hsematoxylin may be used either for fresh material, or for sec- 

 tions which have been previously hardened with alcohol, or with 

 picric or chromic acid. In the latter case the sections must be 

 washed repeatedly in distilled water to remove every trace of the 

 acid, which, if present, would interfere with the proper action of 

 the hsernatoxylin. If the section becomes too deeply stained, as 

 sometimes happens when the alum-hsematoxylin is used, the 

 excess of colouring-matter may be removed by washing with a 

 solution of alum in water. 



Sections stained with alum, or with Kleinenberg's hsematoxylin, 

 are to be mounted in Canada balsam, or Dammar ; those stained 

 with the ammoniacal solution are to be mounted in glycerine. 



Hoffmann's Blue. Used in solution in dilute alcohol slightly 

 acidified with acetic acid : it is a useful reagent, inasmuch as it 



