APPENDIX 141 



wood and the sliells of nuts may require several days in the oven, 

 during' which time it is advisable to change the macerating fluid 

 once or twice. Boiling small slivers of wood before placing them 

 in the acids drives out the air and accelerates the maceration 

 process. The macerated tissue is carefully washed in distilled 

 water to remove as much of the acid as possible and can then 

 be transferred to 50% alcohol for future study. Often effective 

 results may be secured by staining the isolated cells in safranin. 

 For class use, it is only necessary to agitate the alcoholic sus- 

 pension of cells and to add a drop witli a pipette to a slide in 

 order to secure a fairly representative "sample" of the desired 

 cell types. Permanent preparations of macerated tissue are 

 easily made by placing small quantities of cells in water on a 

 slide, evaporating the excess water on an electric hot-plate and 

 mounting in glycerine-jelly. Circular cover-glasses should be 

 used, the edges of which can be sealed with some type of cement 

 which prevents drying out and the entrance of air. 



Special Keagents 



1. Phloroglucin and Hydrochloric Acid. — The addition of 

 these reagents produces a red color in the walls of sclereides, 

 lignified fibers and tracheary elements (cf. Exercises VIII, IX, 

 and X). The stain is not permanent but nevertheless is ex- 

 tremely useful in demarcating the thick walls of certain types of 

 cells. A saturated solution of phloroglucinol should be pre- 

 pared in 95% alcohol. IMount the section or tissue fragment 

 directly in a drop of this reagent on the slide and add a cover 

 slip. Then introduce a drop of concentrated hydrochloric acid 

 at the edge of the cover slip. Great care should be taken to carry 

 out this procedure some distance away from the microscope. 



2. Potassium Iodide (IKI) and Sulphuric Acid. — This is a 

 specific test for cellulose. Mount the sections in the potassium 

 iodide (1 gr. iodine and 3 g. potassium iodide in 300 cc. of 

 distilled water, according to Rawlins, 1933) and add a cover slip. 

 The introduction of a drop of 65% sulphuric acid will cause 

 cellulose walls to turn blue in color. 



