154 
METHODS IN PLANT HISTOLOGY 
seconds. Other things being equal, the best lantern slides are made 
by reduction of larger negatives and the poorest by enlargement 
from smaller negatives. 
The superiority of the larger negative is easily demonstrated. 
With a 5X7 camera, make a negative of some elaborately ornamented 
building, making the building just cover the plate. Then, with a 
3iX4J camera, make a similar negative, so that the building just 
covers the plate. Make lantern slides from both negatives. While 
the building, as it appears on the lantern slide, and on the screen, 
is of the same size in the two cases, the one from the 5X7 negative 
will show much finer detail. The same principle holds true for 
all kinds of plant subjects. The small cameras are easy to carry, 
make good views of interesting bits of scenery, on a tripod, well 
stopped down, will do some fairly good scientific work; but for 
real scientific investigation, take a 5X7. If you are fond of work, 
or can afford to have someone else carry the heavy load, take an 
8X10. 
3 Copying Illustrations.—It is often desirable to get lantern 
slides from photographs, maps, or pictures in books. Here, it is 
necessary to make a negative and then make the lantern slide from the 
negative. In such cases make a 3^X4 negative and print the lantern 
slide by contact. A lantern-slide plate is good for such copying. 
The exposure will depend upon the light, the character of the print, 
and the amount of reduction or enlargement. Other things being 
equal, the exposure will always be longer in case of enlargement than 
in case of reduction. If an average 5X7 photograph is to be copied 
in good diffuse daylight, with an FI6 stop and a lantern-slide plate, 
try 15 seconds. 
For making a negative of a line drawing, about natural size, 
with a Cramer lantern slide for a plate, at F16, dull day with no 
shadows, try 15 seconds. 
For a diagrammatic line drawing, 16X20 inches, F16, good light, 
Cramer lantern slide for a plate, try 10 seconds. 
If one prefers to use film, Eastman Process film is very good for 
copying line work. With the proper exposure and correct develop¬ 
ment it gives excellent results, the lines appearing clean, sharp, 
distinct, with the background perfectly black in the negative. Use 
the developer suggested by the manufacturer. In copying maps 
and line drawings where dead blacks and pure whites are desired, 
