available data, which indicate that the bean 

 group is particularly sensitive to X rays. Asters 

 also proved to be quite sensitive in this respect, 

 while carnations and gillyflowers were so in- 

 sensitive that doses of 8000 and 16, 000 r had a 

 certain stimulating effect on them. Concerning 

 radiosensitivity, tobacco occupies an intermedi- 

 ate position. 



A careful scrutiny of the voluminous data 

 obtained by the various authors on the physio- 

 logical action of the rays shows completely 

 diverse conclusions. Some authors indicate the 

 existence of stimulating doses; others deny 

 their existence. This would be understandable 

 if it were a question of different varieties, since 

 numerous investigators have established that 

 plants are variable in their sensitivity to X rays. 

 However, contradictory results are reported 

 even when the same species of plant has been 

 investigated. As has already been pointed out, 

 the seeds of Vicia faba are a favorite object in 

 X-ray research. Let us take a look at how 

 various authors evaluate the results of irradia- 

 tion of this plant. Perthes found only a depress- 

 ing effect, Koernicke observed a temporary 

 cessation of growth, Schwarz obtained a typical 

 biological curve of development, i. e. , he found 

 that weak doses of X rays stimulate plant devel- 

 opment, that stronger ones retard it, and that 

 still stronger ones stop development altogether. 

 In the experiments of Altmann, Rokhlin, and 

 Gleikhgevikht a temporary acceleration of de- 

 velopment was observed; this was followed by a 

 leveling off to the rate characteristic of the 

 controls. Gambarov failed to find the stimulat- 

 ing dose for Vicia faba equina which had been 

 established in Iven's experiments. And, finally, 

 Johnson, in repeating the experiments of Patten 

 and Wigoder, was unable to confirm the stimu- 

 lating effect of X rays observed by Patten and 

 Wigoder, despite the most careful reproduction 

 of their experiment. 



Besides, as Rokhlin and Gleikhgevikht pointed 

 out in 1925, Vicia faba is not an appropriate 

 object for the study of the stimulating effects of 

 X rays because its threshold of stimulation is 

 too low. It is so radiosensitive that the weakest 

 doses of radiation cause a retardation of growth 

 and thus complicate experiments. 



Naturally, the question comes up of why 

 experiments dealing with the irradiation of the 

 same plant produce such different results. This 

 is not easy to answer. But if we carefully ana- 

 lyze all of the experiments, we shall see that 

 usually the discrepancies can be explained by 

 an insufficiently accurate measurement of 

 dosage (this applies particularly to that period 

 when dosage was measured in erythemas). The 

 sensitivity of people to X rays varies consider- 

 ably, and to equate an erythema dose to 600 r, 

 as some authors do, is completely inaccurate. 

 In general, it is only in the last few years that 

 we have learned to measure X-ray dosages with 



any great degree of accuracy. Besides this 

 chief shortcoming, we have to take others into 

 consideration. In experiments with Vicia faba, 

 which is the object of investigation of many 

 authors, it is amazing to note the small number 

 of seeds used for irradiation. The reason for 

 this lies in the large size of the seeds, which 

 constitutes a substantial barrier for performing 

 the experiment within the restrictions imposed 

 by the limited field of action of the Coolidge 

 tube. The desire for great accuracy forces the 

 investigators to irradiate the seeds simultane- 

 ously with several dosages, removing petri 

 dishes (which contain seeds) from the field of 

 action of the rays at various intervals of time, 

 in order to secure the most uniform voltage and 

 amperage. It is not surprising then that some 

 authors limited their experiments to 5 to 10 

 seeds of this plant. Despite all attempts to 

 match the seeds in size and weight, it was still 

 necessary to take into consideration the indi- 

 vidual variations, which could have been over- 

 come only by using large numbers of plants. 

 Consequently, the criticism of authors (Schwarz 

 et al) that individual variability of the seeds 

 completely overshadows the effects of the radia- 

 tion is entirely justifiable. Only experiments 

 where the number of plants used is sufficiently 

 great to permit biometric analysis can establish 

 whether changes in size and development result 

 from irradiation. But it is most interesting to 

 note that the very same authors (mentioned 

 above), who categorized the experiments of their 

 predecessors as inconclusive on the basis of an 

 insufficient number of test -objects, used only 

 20 seeds in their experiments. 



A third source of error in the experiments is 

 found in the small variation of dosages. Most 

 authors are content to vary the time of exposure 

 or the distance from the tube, both of which are 

 selected at random. It is very characteristic 

 of authors, who obtain changes from random 

 doses of X rays in experiments of this type, to 

 conclude hastily concerning the existence or 

 absence of stimulating doses. 



Experiments which undertake the investiga- 

 tion of the effect of X rays on plants have still 

 another shortcoming: most of them are incom- 

 plete. The majority of investigators either 

 note only the first phases of development of the 

 irradiated plants and compare them with the 

 controls, or cut them down as soon as the first 

 fruit appears and judge the effect of X rays on 

 this or that plant on the basis of the weight of 

 the green or dried mass, ignoring the fact that 

 Doroshenko (1929) and Tsuryupa* (1934) accurate- 

 ly pointed out that X rays can affect reproduc- 

 tive as well as vegetative organs and that their 

 effect on the former is even more pronounced. 



However, the most serious defect of experi- 

 ments with plant irradiation, as of all experi- 

 ments with stimulation in general, is the pre- 

 conceived notion of the investigator. If the 



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