114 
METHODS IN PLANT HISTOLOGY 
The time required varies with the character of the material and 
the thoroughness of the dehydrating and clearing. If this schedule 
has been followed up to this point, the time will be much shorter than 
most investigators now deem necessary. Fern prothallia infiltrate 
perfectly in 15 to 20 minutes; onion root-tips in 20 to 30 minutes; 
ovaries of Lilium at the fertilization stage, 30 minutes to 1 hour; 
5 or 6 mm. cubes of endosperm of cycads, containing archegonia, 
2 to 2\ hours; median longitudinal sections, 4 or 5 mm. thick, through 
ovulate cones of Pinus Banksiana may require 6 or 8 hours; if serial 
sections through the entire cone are wanted, Miss Aase found that 
the time must be prolonged to 24 or even 48 hours. When one is 
dealing with many lots of the same kind of material, as in research 
work, the time required for infiltration is easily determined. As a 
rule, minimize heat. It is, probably, never necessary to use paraffin 
with a melting-point higher than 52° C. With Land’s cooling device 
sections 1 ju in thickness can be cut from 52° C. paraffin. 
IMBEDDING 
Material may be imbedded in paper trays, watch crystals, or any 
apparatus made for the purpose. The most satisfactory imbedding- 
dish we have used is a thin rectangular porcelain dish glazed inside. 
This dish, called a Verbrennungsschale, is made by the Konigliche 
Porzellan-Manufactur, Berlin, Germany. The most convenient 
sizes are 40X50X10 mm., 68X45X10 mm., and 91X58X15 mm. 
As listed, these dishes are not glazed; care should be taken to indicate 
that the dishes must be glazed inside (innen glasiert). Where these 
dishes are not available, any dishes of convenient size and shape can 
be used. The paper tray, if well made, is as good as anything. Thick 
ledger linen or thin, smooth cardboard make good trays. 
Smear the dish or tray with glycerin or soapy water to prevent 
sticking. Another way to prevent sticking is to put a piece of tissue 
paper in the dish, pour on water and make the tissue paper fit the inside 
of the dish, and then pour on the paraffin with the material to be im¬ 
bedded. The paraffin will not stick to the paper. If several objects are 
to be imbedded in one dish, it is best to have the dish as near the tem¬ 
perature of melted paraffin as possible; otherwise the objects may stick 
to the bottom, and it will be impossible to arrange them properly. 
Hot needles are good for arranging material. Great care should 
be taken not to have the dish too hot, since too high a temperature 
