REAGENTS 
21 
100 c.c. of 70 per cent alcohol. We have used a larger proportion of 
formalin, often as much as 6 c.c. to 100 c.c. of 70 per cent alcohol. 
Results which seem equally good have been secured by adding 4 to 
6 c.c. of formalin to 100 c.c. of 50 per cent alcohol. Material in this 
fixing agent may be left until needed for use. 
/) Formalin Acetic Alcohol.—This combination seems even better 
than the preceding. We use about 5 c.c. of glacial acetic acid and 
5 c.c. of commercial formalin to 90 c.c. of 50 per cent or 70 per cent 
alcohol. 
When one is on a long trip, moving frequently from place to place, 
with little opportunity to make the numerous changes which are 
necessary when using the chromic formulas, this is the best fixing 
agent we have found. It will fix and preserve an amount of material 
equal to its own weight, and the material may be left in the solution 
for months. The reagent is good for almost any material, except 
the unicellular and filamentous algae and fungi, which are more 
satisfactory in media containing no alcohol. 
THE CHROMIC-ACID GROUP 
Chromic acid, or solutions with chromic acid as a foundation, are 
the most generally useful killing and fixing agents yet known to the 
botanist. A 1 per cent solution of chromic acid in water gives good 
results, but it is better to use the chromic in connection with other 
ingredients, such as acetic acid, formic acid, osmic acid, etc. Chromic 
acid does not penetrate well, and this is one reason why it is seldom 
used alone. Unfortunately it precipitates some liquid albuminoids 
in the form of filaments and networks, which may be mistaken for 
structural elements. In botanical work, acetic acid is nearly always 
mixed with chromic acid. The pickles of the dinner table show that 
acetic acid is a good preservative, and that it causes little or no 
shrinking. It penetrates rapidly, and is likely to cause swelling 
rather than shrinking, thus counteracting the tendency of chromic 
acid to cause plasmolysis. The swelling is as bad as shrinking. 
If the proportion of acetic acid is too high, material may even 
break up; but 2 per cent, or even 3 per cent, may be used to 
show the topography of an embryo sac of an angiosperm, or the 
free nuclear stage of the endosperm of a gymnosperm; and for fila¬ 
mentous algae, which are to be mounted whole, 3 per cent is very 
effective. 
