30 Methods in Plant Histology 



heating over a Bunsen ftame. It is not worth while to distil more 

 than is needed for immediate use, since the formic acid soon reappears. 



For filamentous algae and fungi a 3 to 6 per cent solution of the 

 ordinary commercial formalin in water is very good. Material is 

 left in the solution until needed for use. For marine algae sea-water 

 should be used instead of fresh water. Both marine and fresh- 

 water material should be washed for half an hour in fresh water before 

 staining. A 6 per cent solution will fix one-fourth its volume of 

 material. With material like filamentous algae or leafy liverworts, 

 a 10 per cent solution will fix all one can put into the bottle without 

 crowding. 



For class use, material should be washed in water for several 

 minutes, because the fumes are irritating to the eyes and mucous 

 membranes. 



For a study of the origin of vacuoles the following combination 

 is recommended: 



Bensley's Formula.- 



1. Formalin (neutral) 10 .0 c.c. 



2. Bichromate of potash 2 . 5 g. 



3. Corrosive sublimate 5.0 g. 



4. Water 90.0 c.c. 



Make the solution 2, 3, 4, and then add the neutral formalin. 

 Fix about 24 hours. Wash in water, but use the iodine necessary 

 on account of the corrosive sublimate just before staining sections 

 on the slide. 



GENERAL HINTS ON FIXING 



It is very desirable that the fixing agent penetrate quickly to all 

 parts of the object. For this reason material should be in small 

 pieces. The best fixing agents do their best work near the surface 

 of the piece. Of course, filamentous algae and fungi, and delicate 

 objects like fern prothallia and root-tips, are simply thrown into the 

 fixing agent. Alcohol, formalin alcohol, or formalin alone, may 

 penetrate J-inch cubes; but the chromic-acid series, which gives 

 the best results in cytological work, penetrates so poorly that cells 

 more than ^ inch from the surface are not likely to be well fixed. 

 Most objects should be trimmed with a razor so that no part shall 



