APPENDIX A 261 



A concentrated solution of caustic potash in alcohol is some- 

 times used with good effect in the preparation of apical meris- 

 tems, but specimens so treated cannot be permanently kept. 



Potassium Acetate (see Acetate). 



Potassium Bichromate is used in dilute solution in water as 

 a test for tannin, which it colours dark brown : the I per cent, 

 solution in water may also be used for hardening tissues. 

 - Potassium Chlorate is used together with nitric acid as a 

 macerating agent, and as a test for suberin (see below, Schulze's 

 Macerating Fluid). 



Russow's Callus-Reagent (see above, Callus-reagent). 



Safranin. This may be used in solution in absolute alcohol. 

 It is especially adapted for staining sections which have been 

 previously hardened with chromic or picric acid ; it is not so 

 good for those which have been treated with osmic acid. The 

 sections must be well washed in distilled water, and then placed 

 in a small quantity (i c.c.) of the saturated alcoholic solution 

 mixed with an equal volume of distilled water ; they require to 

 be left for several hours in the staining fluid. They must then 

 be removed, and washed for a short time in alcohol ; then they 

 must be placed in absolute alcohol, and kept there until they 

 appear transparent. The sections can now be mounted in dis- 

 tilled water in order to see if the results are satisfactory, or, if 

 they are to be preserved, they must be cleared with oil of cloves, 

 and mounted in Canada balsam or Dammar. 



By this means very successful preparations of the structure of 

 nuclei can be obtained. 



Schulze's Macerating Fluid. One gramme of potassium 

 chlorate is dissolved in 50 c.c. of nitric acid ; or crystals of 

 potassium chlorate may be left to dissolve to saturation in a 

 small bottle of nitric acid. This reagent is to be used only in 

 small quantities, and the process of maceration should not be 

 conducted in near proximity to microscopes, or other metallic 

 apparatus. 



It is used as a macerating fluid for separating the constituents 

 of woody tissues from one another, this result being obtained by 

 the solution of the middle lamella. The tissue to be macerated 

 is cut into small chips, and boiled in the fluid for a short time in 



