180 METHODS IN PLANT HISTOLOGY 



the object is being photographed can be accomphshed by watching the 

 action through the inspection ocular and using the fine adjustment of 

 the microscope as necessary. 



Because of the running of the mechanism in the automatic cameras 

 or the turning of the crank in the hand-cranked model, it is necessary 

 that the support for the camera be very rigid. In one set up used by 

 the writer the camera is braced with heavy two-by-fours and held in 

 place by large bolts. 



The Ughting system must be arranged with care. Strong illumina- 

 tion is needed for normal speed work as in the photographing of 

 zoospores and gametes of the algae, or in photographing the movement 

 of the cytoplasm in a cell of Elodea. It is necessary to have sufficient 

 light to give ample exposure in the brief period of approximately ^\ of 

 a second that the camera shutter is open when making 16 frames per 

 second. If too much light is used the living cells may be damaged. A 

 water-cooling cell should always be used between the light and the 

 mirror of the microscope. It may be advisable to use the superspeed 

 panchromatic film as this is approximately three times as sensitive to 

 artificial light as is the regular panchromatic film. In making tune- 

 lapse pictures as in photographing the growth of the hyphae of a 

 fungus with perhaps one frame exposed every three or four minutes 

 the amount of light that is used may be very small. Each frame is in 

 reality a time-exposure in any time-lapse mechanism in which the 

 shaft of the camera is turned continuously at a very slow rate. No 

 exact information can be given in regard to the amount of light that 

 will be necessary for a correct exposure. This must be determined by 

 experiment. Upon the basis of numerous experiments one can build 

 up in time an experience that will make it possible to estimate the 

 amount of light that will be needed for any subject. At the beginning 

 of each experiment it will be well to expose a foot or two of film on the 

 subject and then remove the film and develop it as a negative. If the 

 strip shows good quality as a negative, it is safe to assume that the 

 exposure is correct and that the reversal positive will have good qual- 

 ity when it is returned from the processing station. If this procedure is 

 followed, it will be necessary that the camera and microscope be setup 

 in a dark room, so that the strip of film can be removed from the roll 

 without fogging the rest of the film. 



Motion picture photomicrographs find one of their most valuable 

 applications in making possible the slowing down of action that is too 



