32 
METHODS IN PLANT HISTOLOGY 
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 mitochondria or 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 alcPhol, 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 X V inch from the surface are not likely to be well fixed. 
Most objects should be trimmed with a razor so that no part shall 
be more than T V inch from the surface. Even then, it must be remem¬ 
bered that a waxy or cutinized or suberized surface presents an almost 
impassable barrier to the chromic series. 
Some objects, although small, cause trouble in various ways. 
Many buds are hairy and will not sink; if such things are dipped 
