92 
METHODS IN PLANT HISTOLOGY 
Delafield’s haematoxylin, and various other stains might be tried. 
In double staining it is usually best to combine a basic with an acid 
stain. Green and red make a good contrast, but a section stained 
with iodine green and safranin would be a failure, because both 
stains would stain the xylem and neither would stain the cellulose. 
Both stains are basic. Red lignin and green cellulose could be secured 
by using safranin and acid green. Green lignin and red cellulose, 
as already indicated, can be got with iodine and acid fuchsin. 
The Time Required for the different processes varies greatly, 
and the time required for a subsequent process is often more or less 
dependent upon the time given to processes which preceded it. 
Good mounts of sections of the petiole of Nuphar advena have been 
secured from material which had been cut, fixed, stained in safranin 
and Delafield’s haematoxylin, and mounted in balsam, the entire 
time being less than 30 minutes. This is an extreme case, and 
nothing is gained, except time, and the saving of time is apparent 
rather than real, for the histologist always has something to do while 
the sections are in the stain. 
Preserved, Fresh, and Dry Material.—If sections are to be cut 
from material preserved in formalin, the piece should be washed in 
water, since the odor is annoying and the fumes are injurious to the 
eyes. 
The sections are placed in the stain from water. Sections from 
alcoholic material are transferred directly to the stain. If the 
material is in a mixture of alcohol and glycerin, the sections should 
be washed in water or 50 per cent alcohol until the glycerin has been 
removed before transferring to the stain. 
Some material cuts well when fresh, but cuts with difficulty when 
preserved. On the other hand, some material cuts well when pre¬ 
served, but hardly at all when fresh. Some material which is too soft 
to cut when fresh can be cut with ease after it has been in formalin 
alcohol for a week or more. 
Very hard material, like oak, hickory, maple, etc., should be 
boiled in water and treated with hydrofluoric acid before any section¬ 
ing is attempted. Cut the material into blocks suitable for sections 
and boil in water for several minutes; then transfer to cold water and, 
after several minutes, repeat the boiling. The alternate boiling and 
cooling, which should be repeated several times, drives out the air. 
Transfer to equal parts of commercial hydrofluoric acid and water. 
