112 
METHODS IN PLANT HISTOLOGY 
alcohol and xylol was interpolated; in the second edition of this 
book three grades were placed between the absolute alcohol and 
xylol. It is undoubtedly better to make the transfer still more 
gradual. The following series seem to be safe, 2§, 5,10,15, 25, 50, 75, 
and 100 per cent xylol. These mixtures of absolute alcohol and xylol 
can be made with sufficient accuracy without measuring in a gradu¬ 
ate. The 50 per cent grade is made by mixing equal parts of abso¬ 
lute alcohol and xylol; the 25 per cent, by adding to the 50 per cent 
an equal volume of absolute alcohol; make the 10 per cent grade 
from the 25 per cent by adding a little more than an equal volume 
of absolute alcohol; in the same way, make the 5 per cent from the 
10 per cent, and the 2\ per cent from the 5 per cent. The different 
grades may be kept in bottles and may be used repeatedly. A couple 
of drops of safranin dissolved in absolute alcohol, added to the 50 
or 75 per cent xylol, will color the material a little and will often be 
helpful in orienting after the imbedding in paraffin. 
About 2 or 3 hours is enough for each grade. The pure xylol 
should be changed once or twice. Throughout the dehydrating and 
clearing it is a good plan to keep the material in Number 4 shells, 
which are made from glass tubing about 25 mm. in diameter. 
Other clearing agents may be used, but the process must be just 
as gradual. 
THE TRANSFER FROM CLEARING AGENT TO PARAFFIN 
This should also be a gradual process. The most convenient 
method is to place a small block of paraffin in the pure clearing agent 
with the material, but the block of paraffin should not rest directly 
upon the objects. Dr. Land uses coarse wire gauze, cut into strips 
about 15 mm. wide and tapered at both ends. The strip is then bent 
so that the pointed ends rest upon the bottom of the Number 4 shell, 
while the middle portion forms a flat table upon which the paraffin 
may rest. Dip the wire gauze table into xylol and then slip it care¬ 
fully into the Number 4 shell. The table portion should be 10 
or 15 mm. above the material, and there should be enough xylol 
to extend a few millimeters above the table. Place on the table a 
block of paraffin about equal to the volume of the xylol in the shell. 
The table not only prevents the paraffin from injuring the material by 
mechanical pressure, but insures considerable diffusion before the 
mixture of paraffin and xylol reaches the specimens. After 24 hours 
