234 BOTANY. 



is obtained by using a very dilute, watery solution, and allow- 

 ing the sections to remain for twenty-four hours or so in the 

 staining mixture. 



Hsematoxylin and carmine preparations may be mounted 

 either in glycerine or balsam. (Canada balsam dissolved in 

 chloroform is the ordinary mounting medium.) In using 

 glycerine it is sometimes necessary to add the glycerine grad- 

 ually, allowing the water to slowly evaporate, as otherwise 

 the specimens will sometimes collapse owing to the too rapid 

 extraction of the water from the cells. Aniline colors, as a 

 rule, will not keep in glycerine, the color spreading and finally 

 fading entirely, so that with most of them the specimens must 

 be mounted in balsam. 



Glycerine mounts must be closed, which may be done with 

 Canada balsam as already described. The balsam is best kept 

 in a wide-mouthed bottle, specially made for the purpose, which 

 has a glass cap covering the neck, and contains a glass rod for 

 applying the balsam. 



Before mounting in balsam, the specimen must be completely 

 freed from water by means of absolute alcohol. (Sometimes 

 care must be taken to bring it gradually into the alcohol to 

 avoid collapsing. 1 ) If an aniline stain has been used, it will 

 not do to let it stay more than a minute or so in the alcohol, 

 as the latter quickly extracts the stain. After dehydrating, 

 the specimen should be placed on a clean slide in a drop of 

 clove oil (bergamot or origanum oil is equally good), which 

 renders it perfectly transparent, when a drop of balsam should 

 be dropped upon it, and a perfectly clean cover glass placed 

 over the preparation. The chloroform in which the balsam is 

 dissolved will soon evaporate, leaving the object embedded in a 

 transparent film of balsam between the slide and cover glass. 

 No further treatment is necessary. For the finer details of 



1 For gradual dehydrating, the specimens may be placed successively in 

 30 per cent, 50 per cent, 70 per cent, 90 per cent, and absolute alcohol. 



