104 METHODS IN PLANT HISTOLOGY 



material in 70 and 85 per cent, a day in each, and then run down to 

 water. 



Mayer^s haem-alum is also a good stain for filamentous algae and 

 fungi which are to be mounted in glycerin. The process, after fixing 

 and washing in water, is as follows: 



1. Transfer to the stain from water. 



It is seldom necessary to stain longer than 10 minutes. As a rule, it 

 is better to dilute the stain (about 1 c.c. to 10 c.c. of distilled water) and 

 allow it to act for 10 hours or overnight. 



2. Wash in water, 20 minutes. 



3. Ten per cent glycerin until sufficiently concentrated. 



4. Mount and seal. 



Eosin is a good stain for many algae and fungi which are to be 

 mounted whole, if sharp outlines rather than cell contents are to be 

 brought out. After material has been fixed and washed in water, run it 

 up to 85 per cent alcohol and back to water. Stain in an aqueous solu- 

 tion of eosin for 24 hours; pour off the eosin, which can be used repeat- 

 edly, and pour on a 1 or 2 per cent solution of acetic acid in water. 

 Pour this off and pour on some more of the acid, until very little stain 

 washes out. The process may require 2-5 minutes. Then place in 

 10 per cent glycerin containing about | per cent acetic acid, and allow 

 the glycerin to concentrate. The acetic acid is to prevent the stain 

 from washing out. When the glycerin has reached the proper concen- 

 tration, mount and seal as before. 



The following is a rapid method for forms like Aspergillus and 

 PenicilUum: Fix in 100 per cent alcohol about 2 minutes; stain in 

 aqueous eosin 5 minutes; wash in water about 1 minute; fix in 1 per 

 cent acetic acid 1 minute; then mount directly in 50 per cent glycerin 

 to which about 1 per cent acetic acid has been added. It is hardly 

 worth while to try this method with forms which have large cells; they 

 are sure to collapse. If a form like Eurotium passes through the earher 

 processes without danger, but collapses when put into the 50 per cent 

 glycerin, put it into the 10 per cent glycerin and allow the glycerin to 

 concentrate. 



Mounting without fixing or staining. — It is sometimes desirable to 

 retain the natural color of an object. The chlorophyll green can usu- 

 ally be preserved by mounting directly in glycerin without any previ- 

 ous fixing. Other colors also are often preserved in this way. Moss 

 protonema makes beautiful preparations by this method. If possible, 



