1915] 



OVERHOLTS STUDIES IN THE POLYPORACEAE 679 



razor with an outward stroke of the finger. The sections are 

 placed in a drop of 7 per cent KOH solution on the slide. This 

 immediately expands the hyphae of the tissue to their normal 

 size. The KOH solution is then drained off and a drop of 

 stain added. 



Staining and mounting. — I have tested a considerable num- 

 ber of the more common stains and so far I have failed to 

 find one that gives universally good results if the sections are 

 to be made into permanent mounts. For temporary mounts 

 there is nothing superior to a 1 per cent water solution of 

 eosin, but when sections so stained are mounted in glycerin 

 the color soon completely disappears. The same strength 

 solution of alcohol eosin (in 95 per cent alcohol) often gave a 

 good permanent stain but quite as often it, too, faded out in 

 the course of several weeks, and when used it gives a pre- 

 cipitate that must be washed off with water before the cover 

 glass is applied. Why this stain should remain permanent 

 in some cases and not in others is a question that has not 

 been answered. It may be due to the KOH that remains on 

 the slide and in the sections, but flooding the sections with 

 water after draining off the KOH solution did not seem to 

 have any beneficial effect. Different strengths of alcohol were 

 used in preparing the stain, but with alcohols weaker than 

 95 per cent the stain disappeared even more quickly and the 

 precipitation obtained was so great that such stains were of 

 no value. From the facts observed it seems more reasonable 

 to suppose that the difference may be in the tissue of the 

 fungus rather than in the stain or the glycerin. A solution con- 

 taining equal parts of a 1 per cent water solution and a 1 per 

 cent alcoholic solution of eosin gave no better results. 



Magdala red, Congo red, neutral red, acid fuchsin, methylen 

 blue, and saffranin T were used, and of these, only the last 

 one gave a permanent stain and it has been used in a large 

 part of the work. It is a rapid stain, though probably not 

 quite so rapid as alcoholic eosin, and it is well to leave the 

 stain on the sections for about one minute. A 1 per cent 

 alcoholic solution was used, the stain being dissolved in 95 per 

 cent alcohol. When a drop of this stain is added and drained 



