38 
METHODS IN PLANT HISTOLOGY 
used with immersion lenses is not needed for clearing or for preced¬ 
ing infiltration with paraffin. It is claimed that material cleared in 
cedar oil does not become so brittle as that cleared in xylol or chloro¬ 
form. 
Dr. E. J. Krause has used cedar oil extensively in clearing large 
objects—strawberries and gooseberries either whole or cut in two, 
sections of apple 2 to 4 mm. thick, and similar objects. This method 
is proving valuable in vascular anatomy, some material showing the 
course of bundles very clearly in pieces so large as centimeter cubes. 
Xylol can be used in the same way, but is so volatile that speci¬ 
mens often dry up. Dr. Land suggests equal parts of xylol and 
carbon disulphide for clearing large objects which are to be examined 
without sectioning. 
Clove Oil.—This is an excellent agent for clearing sections and 
small objects just before mounting in balsam. It clears more readily 
than xylol. When the absolute alcohol has deteriorated so that xylol 
no longer clears the sections, clove oil may still clear with ease. 
While clove oil will clear from 95 per cent alcohol, it is better to use 
absolute. Since preparations cleared in clove oil harden slowly, it is 
a good plan to treat them with xylol before mounting in balsam. 
Gentian-violet is somewhat soluble in clove oil, and this fact makes 
it possible to secure a beautiful differentiation, because the stain 
is extracted from some elements more rapidly than from others. 
The stain may be extracted completely from the chromosomes 
during the metaphase and still remain bright in the achromatic 
structures. After the desired differentiation has been attained, the 
preparation should be placed in xylol to remove the clove oil, since 
the continued action of the clove oil would cause the preparation to 
fade. Do not use a Stender dish for clove oil, but keep it in a 50 c.c. 
bottle. Put on a few drops, and immediately drain them off in such 
a way as to remove the alcohol as completely as possible. Then 
flood the slide and pour the clove oil back into the bottle, repeating 
the process until the proper differentiation has been reached. Re¬ 
place the clove oil with xylol and mount in balsam. With stains 
not soluble in clove oil, the xylol is not necessary, except to facilitate 
the hardening of the preparation. 
Clove oil may be used in removing the celloidin matrix from 
celloidin sections. It is useless as an agent to precede infiltration with 
paraffin. 
