140 BROWN: WoopDs FOR MICROSCOPIC STUDY 
may be sufficient; but for general work, longer periods up to two 
hours, giving a heavy but not too opaque stain, are desirable. De- 
hydration is accomplished by washing quickly in 95 per cent alco- 
hol, then successively in absolute alcohol and xylol. The sections 
are mounted in dammar or balsam. 
Sections which tend to curl badly after cutting, as in case of 
many woods with thick-walled elements, may be placed, as soon 
as cut, between two glass slides and allowed to dry before staining. 
In most cases, the section may then be placed free in the stain, 
but occasionally it may be necessary to proceed with one or more 
steps of staining before removing from the slides. 
For a number of purposes, the above process, with slight 
modification, may be used successfully in staining the soft cellulose 
tissues of the bark; but for this purpose Congo red is superior to 
safranin as a counterstain. Where shrinkage due to dehydration 
is not too great and the cell contents stain black, as in Malus or 
Pyrus, preparations showing clearly such details as the reticulate 
thickenings, pits, and even protoplasmic bridges through the 
pit-membranes of the hypodermal ‘collenchyma may be obtained 
by the following process :— 
I. Sections 6 w in thickness are cut from green material col- 
lected in winter, to show pits and protoplasmic bridges in section, 
or 10 uw in thickness to show pits and reticulations in surface view. 
2. Place for five hours in 2.5 per cent aqueous solution of 
iron-alum. 
_ 3. Wash five minutes. 
4. Stain about twelve hours in 0.5 per cent aqueous solution 
of haematoxylin. 
5. Wash five minutes. 
6. Differentiate in a 2.5 per cent iron alum solution until 
sections are gray. 
7. Wash three hours. 
8. Stain in a saturated aqueous solution of Congo red one to 
five minutes for pits in section, ten to thirty minutes for pits in 
surface view, one to two hours for reticulation of thin end-walls. 
9. Dehydrate in absolute alcohol one minute. 
10. Clear in xylol one minute. 
11. Mount in dammar. 
