FREEHAND SECTIONS 
93 
From 1 to 3 weeks will be enough for most woods. Some oaks, ebony, 
apple, etc., may require a longer time and the acid may be used pure. 
One week in 25 per cent acid may be enough for corn stems. Wash 
thoroughly in water for a day or two. Then leave in equal parts of 
30 per cent alcohol and glycerin for several days before cutting. 
Material may be left indefinitely in the mixture of glycerin and 
alcohol. 
An article by Dr. La Dema M. Langdon, dealing with the prepara¬ 
tion and sectioning of hard, woody tissues, appeared in the Botanical 
Gazette of July, 1920. By her method, hard, woody tissues are 
softened so that they cut readily and can even be imbedded in paraffin 
successfully. 
OBJECTS MOUNTED WITHOUT SECTIONING 
Fern Prothallia, mounted without sectioning, make very useful 
preparations. Select desirable stages and fix in chromo-acetic acid 
for 10 to 24 hours; wash in water for 3 or 4 hours, changing the water 
frequently; stain in Delafield’s haematoxylin for 5 to 30 minutes; 
wash in slightly acidulated water for a few seconds, and then wash 
thoroughly in pure water. The prothallia must now be brought 
through a graded series of alcohols, 15,35,50,70,85,95, and 100 per cent 
being sufficiently close to prevent plasmolysis. Then use mixtures 
of alcohol and xylol, 3 parts absolute alcohol and 1 part xylol, 
2 parts alcohol and 2 parts xylol, 1 part alcohol and 3 parts xylol, 
and then pure xylol. Then bring the sections into a mixture of 
xylol and balsam, using at least 10 parts of xylol to 1 of balsam. If 
left in a shell, without corking, the xylol will soon evaporate, so that 
in a few days the prothallia may be mounted. Use the balsam in 
which the material has been standing, because any other balsam may 
have a different concentration. At every step in the process the 
prothallia should be examined under a microscope, so that any 
plasmolysis may be detected. If each succeeding step is tested with 
a single prothallium, a general disaster may be avoided. If plas¬ 
molysis takes place, weaken the reagent and try another prothallium. 
When a safe strength is found, bring on the bulk of the material, and 
use the same method with succeeding steps. The dangerous places 
are likely to be the transfer from alcohol to xylol and the transfer 
from xylol to balsam. The process is tedious, but the mounts are 
very firm and durable. The Venetian turpentine method is less 
