noted neither acceleration nor retardation of 

 development; consequently, he assumed that the 

 one exception was due to chance and did not 

 attach any significance to it. In further experi- 

 ments where Czepa used stronger dosages (150 

 and 300 H), the rate of seed germination did 

 not diminish at all, in fact plants which had 

 received 150 H actually exceeded the controls. 

 Czepa did not continue nor intensify his investi- 

 gations, although his results show that stimu- 

 lating doses lie somewhere between 25 and 150 

 H doses of the rays. On the contrary, as a 

 result of his experiments he came to the con- 

 clusion that stimulating doses do not exist for 

 Vicia faba , Vicia sativa , Phaseolus vulgaris , 

 and lettuce. 



Martius, in 1924, also failed to find a stimu- 

 lating dose in his experiments in which he was 

 trying to ascertain the relationship between the 

 action of the rays and their intensity. Using 

 non-filtered rays of high intensity (130 kv, 

 4 ma) he observed, that radiation of only 1. 9 

 seconds with a focal distance of 10 centimeters 

 was sufficient to halt development. 



Geller (1924) posed the question of the 

 constancy of the effect of X rays on young plants 

 with a definite dosage and came up with negative 

 conclusions. Comparing the data of previous 

 investigators he formulated the following con- 

 clusions: 1) X rays either inhibit or accelerate 

 plant development; 2) their action depends: 

 a) on the dose, b) on the species and X-ray 

 sensitivity, c) on the internal and external con- 

 dition of plants (vigorously growing plants are 

 more sensitive than slowly growing ones or 

 dormant seeds; and the more favorable the ex- 

 ternal environment the greater will be the effect 

 of the rays), d) on the place or area which is 

 being irradiated; 3) since the action depends on 

 various factors, absolute doses for either de- 

 pression or acceleration of the growth rates do 

 not exist; there are only relative doses; 4) the 

 author believes that the permanence of effect is 

 very limited; 5) the initial acceleration of devel- 

 opment is sometimes followed by depression; 

 6) with moderately large doses (those which 

 retard development but which do not kill the 

 plant), microscopic examination does not reveal 

 any particularly obvious injuries to the cells but 

 only retardation of development, and when the 

 doses are small, acceleration of development. 



Gambarov (1925) who tried to surround his 

 experiments with the most thorough precautions, 

 also came to the conclusion that stimulating 

 doses do not exist. From a large number of 

 seeds of Vicia faba equina he selected several 

 hundred which were identical in weight and out- 

 ward appearance. After soaking the seeds for 

 36 hours in water, he transferred them to a 

 specially constructed box with sawdust. The 

 bottom and two narrow sides of this box were 

 made from zinc, while the wide sides were 

 glass. The root length of the irradiated and the 



control plants was measured daily through the 

 glass with a millimeter rule for 12 days. In 

 addition, the time of appearance of lateral roots 

 was noted. Despite the fact that Gambarov used 

 the so-called "stimulating" doses, i.e., 1, 2, 

 3, 4, 5, and 10 HED, not only did he fail to 

 observe acceleration of growth, but he actually 

 obtained the contrary effect because plant 

 development was retarded by these dosages. 



Iven (1925) published a detailed and thorough 

 article on the action of X rays in which he pre- 

 sented the results of his experiments with seeds 

 of Vicia faba in dry and turgid conditions. The 

 irradiation was conducted with ever-increasing 

 dosages of X rays expressed in HED, ranging 

 as follows: 1/250, 1/100, 1/10, [1/2], 1, 5, 10, 

 18, and 22. When doses of 1/250 to 1/2 HED 

 were used on dry seeds, acceleration of germi- 

 nation was noted. On a graph, it was possible 

 to observe first a gentle and then a sharp rise 

 (from 1/20 to 1/2 HED). Beginning with 1/2 

 HED the curve gradually begins to decline. 

 Consequently, Iven's experiments confirm that 

 the stimulating effect of X rays on the first 

 stages of plant development follows the Arndt- 

 Schutze Law. Ten or 20 days later, however, 

 depending on the intensity of growth and external 

 conditions, the difference between the irradiated 

 plants and controls tends to disappear. On the 

 other hand, those plants which exhibited growth 

 retardation because of the action of larger doses 

 were unable in the course of their development 

 to catch up with the controls; the retarding 

 effect of rays is retained. 



When Iven used turgid seeds, the maximum 

 rise of the curve occurred at 1/100 HED. These 

 parallel experiments with dry and soaked seeds 

 demonstrated the significance of the condition 

 of the plant with respect to its sensitivity to 

 X rays. 



The effect of X rays on developmental 

 processes became apparent in Iven's experi- 

 ments after a definite interval of time. Differ- 

 ences between the irradiated and control plants 

 showed up in the growth of stems and in the 

 time required for the appearance of the first 

 leaf. With stimulating doses the first leaf 

 appeared earlier than in the controls, while 

 larger doses retarded the appearance of leaves. 

 The retardation was proportional to the dosage. 

 Finally, when dry seeds received doses of 22 

 HED, no leaves appeared at all, stems and roots 

 were shorter, and roots showed brownish pig- 

 mentation. In addition, they lacked lateral 

 roots. When Iven exposed soaked seeds to 

 X rays, all of these phenomena appeared with 

 smaller doses than were required for dry seeds. 



Between 1924 and 1926 Ancel published a 

 series of papers in which she attempted to 

 clarify the question of the existence of stimu- 

 lating X-ray doses for certain plants of the 

 bean family, especially Phaseolus and Lens 



s 



