108 
METHODS IN PLANT HISTOLOGY 
which have begun to divide may complete the division, although the 
reagent might hinder nuclei from entering upon division. By 
treating for 20 minutes to 1 hour with Flemming’s weaker solution, 
or with a chromo-acetic solution containing a much smaller proportion 
of osmic acid, the killing will be greatly accelerated and the proportion 
of nuclei in division will be correspondingly greater. If filamentous 
Fig. 21. —Spencer rotary microtome with electric motor and Land’s apparatus for temperature 
control. 
algae are placed for 10 or 20 minutes in a chromo-acetic solution con¬ 
taining a little osmic acid, all the advantages of immediate killing 
will be secured. Material is then transferred to chromo-acetic acid 
containing no osmic acid. The short treatment with an osmic solu¬ 
tion is not likely to cause any serious blackening. 
Take the killing and fixing fluids into the field. If one waits 
until the material is brought to the laboratory there may be some 
fixing, but it will, in many cases, be too late to do much killing. 
Material which has begun to wilt is not worth fixing. Material like 
