334 RADIOISOTOPES IN BIOLOGY AND AGRICULTURE 



between the cassette and wood to ensure uniform contact between film 

 and bone. The assembly is kept at refrigerator temperatures for the 

 duration of the exposure. 



4. Upon completion of exposure, the film is processed. 



PLANT MATERIAL. With fresh material, the plant may be blotted, 

 pressed flat, and then placed on the film under safehght conditions with a 

 thin piece of cellophane or Pliofilm between the emulsion and plant to 

 avoid chemical effects. The film and sample can be held in contact for 

 exposure by means of an X-ray cassette with glass plates or any conven- 

 ient press. When desired, the whole plant or parts thereof can be dried 

 between blotting paper under pressure to produce a sample that allows 

 uniform contact with the film. Roots tend to stick to blotting paper, and 

 the use of glass cloth has therefore been suggested (25). Overheating 

 should be avoided, since this tends to make the plant material brittle. 

 After drying, the sample should be removed from the original blotting sur- 

 faces so as to avoid contamination from any radioactive material exuded 

 during the drying-pressing operation. The material may be taped down 

 on the fresh blotting paper to minimize movement and covered with 

 Pliofilm or cellophane to protect the emulsion. Exposure and photo- 

 graphic processing are done as already described. 



HISTOLOGICAL SECTIONS [after Fitzgerald et al. (10)]: 



1. The tissue is fixed, dehydrated, embedded, sectioned, and mounted 

 on a glass slide "subbed" with albumin-glycerin or gelatin to ensure good 

 adhesion. 



2. To prevent chemical effects of tissue on film, the section or emulsion 

 is dipped in 1 per cent Parlodion in amyl acetate, drained, and dried. 



3. The section on the glass slide is placed against the emulsion surface 

 of a 1- by 3-in. glass shde. 



4. The shdes are aligned and held together with a clamp for exposure 

 in a lighttight box at refrigerator temperatures. 



5. After exposure, the emulsion is dipped in amyl acetate for 5 min, 

 followed successively by 95 per cent alcohol, 70 per cent alcohol, 50 per 

 cent alcohol, and water in order to remove the Parlodion layer. 



6. The film is processed. 



7. Embedded tissue is deparaffinized, and the tissue stained. 



8. The autogram and section can be examined separately or together 

 under the necessary magnification. 



Buie et al. (26) have described a method that permits separation of the 

 tissue and emulsion during photographic processing or staining but still 

 allows alignment of the autogram and section at will for simultaneous 

 observation. This is accomphshed by mounting the tissue section at one 

 end of a plastic, flexible cover slip. The opposite end is cemented with 

 beeswax and rosin to the emulsion side of a photographic plate. The 



