14 PRACTICAL BOTANY. 



After treatment with the aqueous solution, the sections 

 should be washed in distilled water, and after treatment 

 with the alcoholic solution in dilute alcohol; the sec- 

 tions, in both cases, should be mounted in glycerine. 



Another method of clearing, which is especially re- 

 commended for obtaining good preparations of growing 

 points, is to treat sections with calcium chloride. The 

 sections are placed on a slide in a drop of water, and 

 are then covered with some dry powdered calcium 

 chloride ; the slide is then warmed over the flame of 

 a spirit-lamp until the water has nearly all evapo- 

 rated; a drop or two of water is now placed on the 

 sections, and they are to be mounted in glycerine. 



In the case of tissues, which have been hardened in 

 alcohol, with or without treatment with other hardening 

 agents, another method of clearing may be used. The 

 sections, after staining, if that is desired, should be placed 

 for a few minutes in absolute alcohol ; they should then 

 be transferred to a watch-glass, containing either a mix- 

 ture of turpentine and creosote (four parts of the former 

 to one of the latter), or some oil of cloves ; sections 

 which have been stained with aniline dyes are best 

 cleared by cedar-wood oil ; they should be left in this 

 for a short time, until they appear to be quite trans- 

 parent, and should then be mounted in a drop of Canada 

 balsam or Dammar. 



Mounting. For the observation of the coarser 

 features of the histology of plants, it suffices to mount 

 the sections in a drop of water, or, in certain cases, in a 

 drop of alcohol. This is the only possible method when 

 micro-chemical observations have to be made. Sections 

 of objects which have been hardened, or otherwise 



