148 
METHODS IN PLANT HISTOLOGY 
frequently use lantern-slide plates for tests and for small photo¬ 
micrographs. The Cramer lantern slides and contrast plates of 
larger sizes have the same speed and, consequently, one can determine 
the length of exposure by using a cheap lantern slide. In making 
tests, it will save both time and money to expose for 5 seconds and 
then push in the dark slide so as to cover a part of the plate; then 
expose 5 seconds longer and push the slide in a little farther, etc. 
In this way you can make 4 or 5 exposures on a lantern-slide plate 
showing exposures of 5, 10, 15, 20, and 25 seconds, the first exposure 
being 5 seconds and the last, 25 seconds. By making several expo¬ 
sures on 1 plate, with the first probably underexposed and the last 
probably overexposed, you can note which exposure is best and will 
waste only 1 plate in getting the time. A print from such a negative 
is valuable, since it enables one to judge very accurately the printing 
quality of the various exposures. 
A slow contrast plate such as mentioned above will prove satis¬ 
factory for photographing some subjects and because of ease in 
manipulation it offers certain advantages for the beginner; but it 
is not the most satisfactory in a majority of cases. It is necessary 
to use a plate which is color corrected when one is using ray filters 
to increase or decrease the contrast between differently stained 
portions of a preparation or to secure greater detail than could be 
obtained without a filter. We have used the Cramer Iso plates and 
the Eastman Standard Orthonon plates a great deal. They are 
orthochromatic, sensitive to a large part of the spectrum, and can be 
used with the various filters, with the exception of the reds. When 
it is necessary to use a red filter, we suggest the Wratten Panchromatic 
plates. 
Professional films are rapidly replacing plates for many phases 
of photographic work. The Eastman Commercial Ortho film was 
used in the making of all the photomicrographs in this edition credited 
to Dr. Sedgwick. This Commercial Ortho film is thick, rather slow, 
and gives a combination of detail and contrast which is very desirable. 
It is heavy enough to lie flat in the Professional Film holders made for 
Professional films. It is strongly orthochromatic and may be used 
with all the filters commonly employed in photomicrography except 
for the reds. If it is necessary to use a red filter in order to make a 
red-stained portion of a preparation appear light, the Eastman 
Commercial Panchromatic film may be used. This film works as 
