126 
METHODS IN PLANT HISTOLOGY 
retains only a faint pinkish color. Wash in 70 per cent alcohol (not 
acid) until the characteristic purple color of the haematoxylin replaces 
the red due to the acid. Stain in eosin (preferably a 1 per cent solu¬ 
tion in 70 per cent alcohol) for 2 to 5 minutes. Dehydrate in 95 per 
cent alcohol for about 5 minutes. Absolute alcohol must not be 
used, unless it is desirable to remove the celloidin matrix. Eycleshy- 
mer’s clearing fluid (equal parts of cedar oil, bergamot oil, and 
carbolic acid) clears readily from 95 per cent alcohol. Mount in 
balsam. 
If serial sections are necessary, arrange the sections upon a slide, 
using enough 70 per cent alcohol to keep the sections moist, but not 
enough to allow them to float. Cover the sections with a strip of 
toilet paper, which can be kept in place by winding with fine thread. 
After the sections have been stained and cleared, remove the excess 
of clearing fluid by pressing rather firmly with a piece of blotting- 
paper. Then remove the toilet paper and mount in balsam. 
With occasional slight modifications, we have used the method 
as presented by Eycleshymer in his classes. Instead of the graded 
series of celloidin solutions, we use a 2 per cent solution, which is 
allowed to concentrate slowly by removing the cork occasionally, 
or by using a cork which does not fit very tightly. The material 
is imbedded when the solution reaches the consistency of a very 
thick oil. If the material is to be cut immediately, we prefer to 
imbed it and fasten it to the block at the same time. The blocks 
should have surface enough to accommodate the objects, and should 
be about J inch thick. White pine makes good blocks; cork is 
much inferior. Place the block for a moment in ether-alcohol and 
then dip into the 2 per cent celloidin the end of the block which was 
left rough by the saw. With the forceps remove a piece of the 
material from the thick celloidin and place it upon the block, taking 
care to keep it right side up. Dip the block with its object first in 
thick celloidin, then in thin, and after exposing to the air for a few 
minutes drop it into chloroform, where it should remain for about 
10 to 20 hours. It should then be placed in equal parts of glycerin 
and 95 per cent alcohol, where it may be kept indefinitely. If the 
material is hard, like many woody stems, it will cut better after 
remaining in this mixture for a couple of weeks. 
The following schedules, beginning with the celloidin sections 
in 70 per cent alcohol, will give the student a start in the staining: 
