300 
METHODS IN PLANT HISTOLOGY 
mother-cells at the top may show the first division, while those at 
the bottom show the second. Determine the stage by examining a 
few mother-cells before fixing. 
From what has been said, it is evident that longitudinal sections 
should be cut to show mitosis. Transverse sections should be cut 
to show the general structure of the anther. It is not necessary to 
cut the stamens into pieces before fixing, since they are easily pene¬ 
trated and infiltrated; in later stages the stamens must not be cut 
into pieces, since the pollen grains and even the pollen mother-cells 
are easily washed out. 
The problem of fixing spore mother-cells has received much atten¬ 
tion. In fixing mother-cells and the two mitoses by which spores 
are formed, investigators have used almost exclusively the chromo- 
osmo-acetic acid solutions of Flemming, some preferring the weaker 
solution and some the stronger. These solutions have been used 
in nearly all of the work of the Bonn (Germany) school. Osterhout 
experimented with forty fixing agents, and then concluded that 
Flemming’s stronger solution was the best. Professor Gregoire and 
his students have made this their principal fixing agent. 
In the third edition of this book we stated that, in spite of the 
weight of authority, we believed the value of solutions with such 
a large proportion of osmic acid had been overestimated and we sug¬ 
gested that half the amount of osmic recommended in Flemming’s 
weaker solution would be sufficient. The weaker solution has 10 c.c. 
of 1 per cent osmic acid in 100 c.c. of the fluid. After an examination 
of thousands of figures in both reduction and vegetative divisions, 
we feel sure that 5 c.c. of the osmic is enough and, perhaps, 3 or 4 c.c. 
would be better. The formula for Flemming’s weaker solution is 
often given as follows: 
f Chromic acid (1 per cent). 25 c.c. 
A \ Glacial acetic acid (1 per cent). 10 c.c. 
(Water. 55 c.c. 
B. Osmic acid (1 per cent)_;. io c.c. 
Keep the mixture A made up, and add B as the reagent is needed 
for use, since the solution does not keep well. One seldom uses this 
reagent in large quantities. About 40 c.c. is as much as one is likely 
to need for any collection of anthers or root-tips. Take 36 c.c. of A 
and 4 c.c. of B. It will be worth while to try 36 c.c. of A and 2 c.c. 
