PLANT MICRORADIOGRAPHY 



narj^ microscopy but quicker and more cm, the specimen being 1 cm from the Be 



easily obtainable without laborious prepara- window; 15 sec. to 1 min. for exposure; 



tion. In addition, freeze-drying of green or holder for object and film is a cylindrical 



moist specimens increases radiotransparency camera moving in a tube at any desired 



and permits shorter exposures. The operating distance from x-ray focus. The specimen is 



conditions in this work were as follows: pressed against a flat fine-grain Lippmann 



projection microscopy; magnification Xlo, film by a spring to a limiting aperture and a 



X20 or X260 by photographic enlargement, brass disk closes the camera (Fig. 4, PI. 1). 



X900 for high resolution film; 7 to 20 kV The use of a vanadium filter is not to be 



and 5 to 10 niA; Mo target and Be window; recommended in these conditions for it 



tube-object distance = 40 cm; vacuum in eliminates the useful CrK/3 line and removes 



cassette; Lippmann film or Maximum Reso- only a small amount of radiation of short 



lution plates; exposure times vary from wavelength. An automatic switch guards 



second to hour, depending on object, dis- against a fall in pressure of the cooling 



tance, voltage, milliamperage, vacuum and water. Control arrangements in the gener- 



speed of films; film employed depends on ator ensure that it functions within the 



magnification wanted and influences expos- prescribed limits of voltage. 



ure time. To obtain greater contrast it is also easy 



At this same time Trillat in France asked to employ in a few cases the small Philips 



a botanist to study with a physicist the generator (1 to 5 kV; 6 to 8 A; Cu anode; 



common problem of a proper handling tech- focus-specimen distance 1.5 to 2.5 cm, but 



nique for plant biological researches. In the observable area is smaller than that for 



order to approach histological field a survey the tube described above; possibility to 



was made to examine optimum conditions evacuate air around object; 1 to 10 min. 



of exposure time, and microradiographic exposure). 



accuracy of very different specimens such as A monochromator can be added when a 



leaves, epiderms, algae, crystalline struc- long exposure is not inconvenient. Relative 



tures, salt and acjueous constitution of to specimen preparation, it is better to cut 



tissue. The detailed technicjue of a very it by freezing microtome in sections from 50 



simple contact method was described by to 100 /x. Then sections are fixed preferably 



Legrand and Salmon (1954) (8) and Salmon with Carnoy's solution during one hour. 



(1956) (9) ; additional details were given Serial sections are impregnated with increas- 



in following publications (10). Then work ing concentrations of alcohol, so that they 



was undertaken with help of this equipment are taken from absolute alcohol for radiog- 



by Manigault and Salmon (1956) (10) con- raphy. Alcohol does not interfere with ob- 



cerning cancer plant tissue development, servations but it is necessary to drain the 



concurrent^ with staining and polarizing section before exposing to the x-ray beam 



technicjues. Results were satisfying enough without avoiding complete desiccation. The 



to assure the great utility of this x-ray results are poorer with formalin fixation or 



method in plant biologJ^ from sections embedded in paraffin although 



Histological Technique for microradio- these methods are usable in case of necessity. 

 graphy (MR) : A summary of details of this However a fresh test section must be corn- 

 contact method is as follows: commercial pared in order to evaluate these different 

 sealed-off tube (Fig. 1, PI. 1); chromium experimental procedures, especially to esti- 

 anode; wavelength 2.28 A; 15 to 20 kV and mate the importance of the haze due to 

 20 to 15 ma; focus-specimen distance of 5 impregnation of water in plant tissue. 



637 



