218 
METHODS IN PLANT HISTOLOGY 
Fix in 1 per cent chromo-acetic acid (1 g. chromic acid and 1 c.c. 
acetic acid and 100 c.c. water) for 24 hours; wash in water 24 hours, 
stain sharply in eosin, transfer to 10 per cent glycerin, and follow 
the Venetian turpentine method. 
Material may be fixed in corrosive sublimate-acetic acid (cor¬ 
rosive sublimate 2 g., glacial acetic acid 2 c.c., and water 100). Use 
it hot (85° C.). One minute is long enough. Wash in water and 
add, a few drops at a time, the iodine solution used in testing for 
starch. At first, the brownish color caused by the iodine will dis¬ 
appear, but after a certain amount has been added the brownish 
color will remain. Stain in eosin or iron-haematoxylin and follow 
the Venetian turpentine method. 
A very rapid method for this and for similar small filamentous 
forms may be added. Forms as large as Thamnidium elegans can 
be mounted successfully by this method. 
1. 100 per cent alcohol, 2 minutes. 
2. Eosin (aqueous), 2 minutes. 
3. 1 per cent acetic acid, 2 to 10 seconds. 
4. Mount directly in 50 per cent glycerin and seal. 
If the material gets through the first three stages without shrinking 
but collapses at the fourth, put it into 10 per cent glycerin and allow 
it to thicken, following the Venetian turpentine method. 
The earlier perithecial stages are more instructive when mounted 
whole; but later stages, even before the formation of the asci, are 
very unsatisfactory by this method, and should be cut in paraffin. 
Penicillium.—This green mold is found everywhere upon de¬ 
caying fruit, upon bread, and upon almost any decaying organic 
substance. Material is even more easily secured than in case of 
Aspergillus , and Penicillium is an easier type for laboratory study. 
Such a satisfactory study can be made from the living material that 
it is hardly worth while to fix and stain. The very rapid method 
described for Aspergillus will furnish good mounts if permanent 
preparations are desired. 
The Erysipheae.—The mildews are found throughout the summer 
and autumn on the leaves of various plants. Some of the most 
abundant forms are Microsphaera alni on the common lilac; Sphaero- 
theca castagnei on Bidens frondosa and other species, on Erechtites 
hieracifolia , and on Taraxacum officinale; Uncinula necator on 
Ampelopsis quinquefolia, and U. salicis on Salix and Populus; 
