and Laboratory Methods. 2203 



QUESTION BOX. 



Inquiries will be printed in this department from any inquirer. 

 The replies will appear as received. 



Li 



No. 28. Why do some crystals polarize and some not ; e. g., common salt, 

 etc ? — J. L. L. 



No. 29. What is a good method for making sections of moss leaves, etc ? — 



W. B. D. 



REPLY TO QUESTION No. 24. 



The following method for Fixing and Flattening Parafhn Sections is a 

 modification of Heidenhain's, and may be found useful where sections are ap- 

 parently hopelessly crumpled. Dr. H. E. Durham (Quart. Jour. Micro. Sci. 3i : 

 1892) says he finds it better and easier than Gaskell's method: 



1. Place sections on a dry slide or one moistened with methylated spirit 

 diluted to 70 per cent, alcohol. 



2. Place slide on warming plate just hot enough to soften, no more — use- 

 less ribbon sections make a good " thermoscope." 



3. With a pipette add a/^7*:/ drops of TO per cent, alcohol ; as the paraffin 

 softens the wrinkles disappear. When the sections are flat, remove excess of 

 alcohol with the pipette (avoid too much alcohol, or sections are displaced ; 

 avoid too little alcohol, or they will not become flat). 



4. Evaporate the alcohol ; warm the paraffin ; dissolve paraffin with xylol, 

 benzol, or 7-8 parts benzol to 1 part of turpentine ; mount in Canada balsam. 



If staining on the slide is desired. Dr. Durham recommends alcohol for fixing 

 rather than any other, because no stained film is left as with collodion, albumen, 

 etc. For other notes see Gage's book on The Microscope, Transactions of the 

 American Microscopical Society, Lee's Vade Mecum, etc. — v. a. l. 



REPLY TO QUESTION No. 27. 

 The formula for Knop's solution, as given by Dassonville,* is as follows : 



Calcium nitrate, ----- l.oo g. 



Mono-potassium phosphate, - - - O.'iS 



Potassium nitrate, - . . . 0.25 



Magnesium sulphate, . . . . 0.25 



Ferric phosphate, . . - . trace. 



Water, - 1000 



Instead of ferric phosphate, I have used in this culture solution a trace of 

 ferric chloride, which appears to work a little more satisfactorily. A method 

 for preparing a concentrated solution of the same nutrient salts is found in a 

 paper by Knop in Landw. Versuchs-Stationen, Bd. XXX, p. 292-294, 1S84. 

 University of Tennessee, Knoxville. Samuel M. BaiN. 



* Rev. gen. de Botanique, t. VIII, p. 285, 1896. 



