174 METHODS IN PLANT HISTOLOGY 



for photomicrographic work. The light should be lined up as accurate- 

 ly as possible. One or more condensing lenses should be inserted be- 

 tween the light and the condenser of the microscope in order to con- 

 centrate the rays. For this, one may use a spherical flask filled with 

 water, or a simple hand reading glass will serve. The condensing 

 lenses of a small stereopticon can be adapted. If a round flask filled 

 with water is used, it will serve both as condenser and heat-absorbing 

 unit. If lenses are used for the auxiliary condensing system, it will be 

 necessary to provide a flat-sided flask or small battery jar with water 

 to absorb the heat and thus protect the slide that is to be photo- 

 graphed. The auxiliary condensing system should be placed in such a 

 position as to project a magnified image of the light source on the iris 

 diaphragm of the condenser of the microscope. 



The slide which is to be photographed is next brought into focus on 

 the ground glass of the camera with the coarse and fine adjustments of 

 the microscope. The substage condenser is focused to obtain critical 

 illumination. This will bring the light to a focus on the section to be 

 photographed. An image of the source of light will now be seen on the 

 ground glass superimposed upon the image of the object. By examin- 

 ing the ground glass of the camera, any further adjustments that may 

 be necessary can be made in order to bring the light source, the auxili- 

 ary condensing system, the substage condenser, the microscope tube, 

 and the camera into perfect alignment. After all of the adjustments 

 have been correctly made, move the substage condenser a very short 

 distance either toward or away from the slide so as to remove the image 

 of the light source from the ground glass. This adjustment should be 

 very slight and will not appreciably affect the quality of the image of 

 the object to be photographed. 



It will now be necessary to decide upon the plate or film to be used 

 for the photograph and it will also be necessary to choose an appropri- 

 ate light filter. The yellow filters which are used in ordinary photog- 

 raphy will be found to be useful, but, if a great amount of photomicro- 

 graphic work is to be done, the worker should have a set of light filters 

 such as the set of 9 Wratten filters for photomicrography sold by the 

 Eastman Kodak Company. This set includes the filters that will be 

 found to be most useful. In choosing the plate or film and the light 

 filter it is necessary to come to a decision in regard to the effect that is 

 desired in the picture. The choice of plate, or film, and filter will de- 

 pend upon whether it is desired to obtain the maximum contrast be- 



