90 
METHODS IN PLANT HISTOLOGY 
Sections from fresh material are fixed in 95 per cent alcohol; 
sections from preserved material are rinsed in alcohol or water before 
staining. The following schedule will summarize the method: 
1. Safranin, 2 to 24 hours. 
2. 50 per cent alcohol, until differentiated. 
3. Dehydrate in 95 and 100 per cent alcohol. 
4. Light green (in clove oil), 3 to 30 minutes. 
5. Xylol: 2 or 3 c.c. of absolute alcohol may be added to each 100 c.c. 
of xylol, if the free light green shows a tendency to precipitate. 
6. Mount in balsam. 
This stain is particularly good for phloem. Since the light green 
is not likely to overstain and does not extract the safranin, the 
combination is a rather easy one. Even the beginner can hardly 
fail to get a good preparation. 
Malachite Green and Congo Red.—I am indebted to Dr. Sharp 
for this method, which has been popular in Professor Gregoire’s 
laboratory at Louvain. 
Sections of fresh material should be treated with 95 per cent 
alcohol and then transferred to water. 
1. 3 per cent aqueous solution of malachite green or methylin blue, 
6 hours or more. 
2. Wash in water. 
3. Congo red, 1 per cent aqueous solution, 15 minutes. 
4. Wash in water. 
5. Rinse in 80 per cent alcohol. As soon as the malachite green or anilin 
blue color appears through the red, transfer quickly to 
6. Absolute alcohol. 
7. Xylol. 
8. Balsam. 
Iodine Green and Acid Fuchsin is another good combination 
for such sections. The stain will be particularly brilliant if sections 
from fresh material are fixed in 1 per cent chromo-acetic acid for 
10 to 24 hours; and then washed for an hour in water. Beginning 
with the sections in water, the procedure is as follows: 
Stain is aqueous iodine green for 12 to 24 hours. Then wash in 
water until the stain is nearly all washed out from the cellulose walls, 
but is still brilliant in the lignified walls. If the stain acts for too 
short a time, the washing-out process necessary to remove the stain 
from the cellulose walls will leave only a pale-green color in the ligni- 
