REAGENTS 
31 
Miss Ethel Thomas recommends this formula for the female 
gametophyte of Pinus. 
d) Corrosive Sublimate and Picric Acid (Jeffrey’s solution).— 
Corrosive sublimate, saturated solution in 30 
per cent alcohol. 3 parts 
Picric acid, saturated solution in 30 per cent 
alcohol. 1 part 
It would be worth while to try other combinations. 
IODINE 
Iodine is well known as an antiseptic. It is also a good fixing 
agent for unicellular, colonial, and filamentous forms. It penetrates 
rapidly. 
To a saturated solution of potassium iodide in distilled water, 
add iodine to saturation. Filter and dilute with distilled water 
until the solution has a rich brown color. For fixing, dilute still 
further to a light-brown color. The solution fixes in 10 to 24 hours, 
but material may be left in it for several days. Wash thoroughly 
in tap water which has stood long enough to give off all excess of air. 
If the staining of the starch does not disappear, a J per cent solution 
of tannic acid in water will remove any excess color. 
FORMALIN 
Formalin is an excellent preservative. It has been mentioned 
already as an ingredient in several formulas. Commercial formalin has 
a strength of 40 per cent. Throughout this book, a 2,4, or 6 per cent 
formalin is understood to mean 2, 4, or 6 c.c. of commercial for¬ 
malin to 98, 96, or 94 c.c. of water, alcohol, or any other ingredient. 
Commercial formalin is sure to contain some formic acid. For most 
purposes, it is neither necessary nor desirable to remove the acid. 
For studying the origin of vacuoles, it is necessary to have neutral 
formalin, which can be secured from commercial formalin by dis¬ 
tillation. Place some sodium bicarbonate in a flask of formalin and 
distil by heating over a Bunsen flame. 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 
