Nov. 5. 1917 Diagnosing White-Pine Blister-Rust from Its Mycelium 283 
which time it may be drawn off and kept to be filtered back into the 
drop bottle. By tilting the watch glass the sections can be grouped 
easily at one side of the watch glass. Then, after the safranin has been 
drawn off, any excess red in the dish may be wiped out with a cloth. 
Care should be 1*aken that the sections do not dry out. The lichtgruen 
should be added as soon as the excess safranin is removed. A muddy 
mixture of red and green results. The lichtgruen replaces the safranin 
quite rapidly, so that a minute is usually the maximum time necessary 
to produce the proper green tint. The writer shakes the watch glass as 
soon as the lightgruen is added, then draws off the red-green mixture, 
and adds a few drops of fresh lichtgruen. The green stain should not 
be allowed to act long enough to wash out too much of the safranin. 
The time required depends on (1) the thickness of the sections, (2) the 
time the sections were stained in safranin, and (3) the strength of the 
lichtgruen solution. The used lichtgruen should be thrown into a waste 
jar. 
(< d ) Clearing and mounting. —After the removal of the green stain, 
absolute alcohol should be added immediately and the watch glass 
rocked or shaken. This absolute alcohol should be drawn off and saved 
in a waste jar, and the sections treated with fresh absolute alcohol for a 
minute or two, the total time depending on the number of sections 
handled at one time. This absolute alcohol should then be replaced by 
clove oil. While in clove oil the sections may be conveniently lifted 
with a small brush and arranged on the slide without danger of drying 
up, and for this reason clove oil is used between absolute alcohol and 
the more volatile xylol. After the sections are arranged, they should be 
rinsed with drops of xylol until the clove oil has been removed. A drop 
of balsam and a warm cover complete the mount. It is advisable to set 
the slide away for a day in the paraffin bath with a heavy lead weight on 
the cover to flatten out the sections. 
(e) Coeor resuets. —The color results in the finished slide vary 
slightly, depending on the amount of safranin which was removed when 
the green stain was acting. A good diagnostic slide for Cronartium 
ribicola should have red host nucleoli and reddish nuclei, red wood cells, 
dead cells, and cork cells. Occasionally resin cells stain a deep red. 
The host cytoplasm and all cellulose walls should be green. The hyphse 
of the parasite stain green, but they stand out well when they are colored 
a greenish pink or greenish red—that is, when the red is not removed 
too far. The nuclei of the parasite should be red. Although the stains 
employed do not result in the differential staining of the host and para¬ 
site, there is no difficulty in distinguishing them. 
(/) Advantages or the method. —The chief advantages of the 
method are its simplicity and rapidity. Permanent record slides from 
a suspected specimen can be completed easily in about two and one- 
half hours from the time the specimens reach the laboratory. Correctly 
