50 PKACTICAL BOTANY 



after treatment with the alcoholic solution in dilute 

 alcohol ; the sections, in both cases, may be mounted 

 in glycerine : or the sections may be treated at once 

 with a mixture of potash solution and glycerine, but 

 in any case the potash must be washed out before 

 mounting as a permanent object. 



If treatment with potash solution does not readily 

 make the tissues transparent, the action of the reagent 

 may be accelerated and intensified by warming over a 

 spirit-lamp. If the action, be too strong, and the tis- 

 sues become too transparent, this may be corrected by 

 neutralizing with acetic acid. 



Another method of clearing, which is used in the 

 preparation 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 evaporated ; a drop or two of water is now 

 placed on the sections, and they are to be mounted in 

 glycerine. 



Another method which has recently come into use 

 and gives good results, especially in clearing growing- 

 points, is by the use of "eau de javelle" (see Appendix 

 A). The object, either fresh, or after hardening in 

 alcohol or picric acid, is mounted under a cover-slip in 

 " eau de javelle " for three or four to ten or fifteen 

 minutes, according to the rapidity of action of the 

 reagent : very gentle warming over a spirit-lamp will 

 quicken the action : it is then to be carefully washed 

 with water, next with dilute acetic acid, a,nd it may 

 finally be mounted in glycerine. 



