146 METHODS IN PLANT HISTOLOGY 
optical axis of the microscope, fit to the guideway a board of the 
necessary thickness, and fasten the camera to this board. It is 
absolutely necessary that the preparation to be photographed and 
the ground glass of the camera should be perfectly parallel. The 
board will save time in securing this parallelism. Cut through the 
board a slot l inch wide and extending to within 6 inches of each end. 
By this means the camera can be clamped with the screw used to 
fasten it to a tripod. Also, a 
piece of metal or hard wood 
may be placed over the horse¬ 
shoe base of the microscope 
and with a bolt, preferably one 
with a butterfly nut, the micro¬ 
scope may be held firmly in 
place. This board, with the 
long slot, will be useful in 
making lantern slides. 
As an illuminant, direct 
sunlight, diffuse daylight, a 
gas-mantle lamp, an acetylene 
lamp, a Mazda bulb, an arc 
light, or any strong light may 
be used. Remove the mirror 
from the microscope and allow 
the light to come directly into 
the optical axis. This mirror 
will not be needed in any pho¬ 
tomicrographic work. 
Let us suppose that we are to make a photomicrograph of a 
vascular bundle and that we are using a 16-mm. objective. If 
only a part of the bundle is shown on the ground glass, remove 
the ocular of the microscope. If the illumination is very uneven 
and shows a “flare spot/’ look at the inside of the tube of the micro¬ 
scope. Probably it was not blackened and the “flare spot” was 
due to reflections. Obviate the difficulty by putting a piece of black 
paper inside the tube. Any modern microscope should have the 
tube well blackened inside. Move the light back and forth and 
sidewise to get the best illumination. An easy way to determine 
whether the light is centered is to close down the iris diaphragm below 
A 
^^ 
l-Z 1 L 
Fig. 29.— A, board for photomicrographic and 
lantern-slide work; B, end view with clips to hold 
negatives; C, side view of block to be used on board 
when making lantern slides. 
