258 
METHODS IN PLANT HISTOLOGY 
subtropical regions, but almost never seen in greenhouses nor even in 
botanical gardens. Formalin alcohol material is easily cut without 
imbedding and is easy to stain. 
The stems of tree ferns require special treatment. With the 
large leaf bases partly cut away with a sharp razor, transverse sec¬ 
tions are easily cut for a con¬ 
siderable distance below the 
apex. Material fixed in for¬ 
malin alcohol cuts very well. 
If fresh material is to be cut, 
the softer portions should be 
flooded with alcohol after each 
section. Farther down, there 
will be a region where sections 
can be cut without any flood¬ 
ing, and still farther down, it 
will be difficult or impossible 
to cut sections across the whole 
stem. Sections 1 or 2 cm. 
thick, cut smooth on the ends, 
may be kept in 95 per cent 
alcohol or in glycerin in large 
glass dishes of the Petri dish 
pattern. Better still, clear 
such sections in xylol and pre¬ 
serve in cedar oil. 
The root .—The roots of 
Filicales develop from a strong 
apical cell. For mitotic fig¬ 
ures and the development of 
the root from the apical cell, 
fix the tip in chromo-acetic acid with a little osmic acid. If the 
development of the root is the principal object, stain in safranin and 
light green, or in the safranin, gentian-violet, orange combination; 
if mitotic figures are to be studied, stain in iron-haematoxylin with 
a very light counter-stain in orange. The comparatively large root- 
tips of Botrychium are excellent for the apical cell and its segments. 
Dicksonia punctilohula can also be recommended; but even the very 
small root-tips of most of our ferns will yield good preparations. 
Fig. 84. —Angiopteris evecta: photomicrograph 
of a transverse section of a root, showing the 
polyarch, exarch siphonostele. Eastman Commer¬ 
cial Ortho film, Wratten E (orange) filter; arc light; 
J. Swift and Son 1-inch lens; exposure, f second. 
Negative by Dr. P. J. Sedgwick. X25. 
