Czeps, and Schindler* (mentioned previously) 

 suffered from many shortcomings, but that their 

 merit lay in the fact that they were the first to 

 point out the many sources of errors due to the 

 inconstancy of plant objects. By his investiga- 

 tions Bersa was trying to show how careful one 

 must be in interpreting the results of experi- 

 ments. The first condition to be observed is 

 to have a sufficiently large number of test ob- 

 jects. In sprouts of Vicia faba , the author 

 measured the length of stems from the ring 

 where the root begins to the growing point and 

 the length of the rootlets from the ring to the 

 tip. With a dose of 0. 05 H a 26% increase in 

 length of the rootlet was observed, but the 

 author did not attach any significance to this 

 since only 10 rootlets were examined. The 

 measurement of control and irradiated rootlets 

 of Sinapis alba did not reveal any significant 

 differences, while a measurement of their hypo- 

 cotyls showed an incontestable acceleration. 

 The following experiments gave less significant 

 or negative results. For instance, although an 

 acceleration of the growth of hypocotyls takes 

 place, this growth depends on enlargement of 

 the cells rather than on cell division, i. e. , the 

 cells of the hypocotyl enlarge greatly as an 

 aftermath of water intake. In general, the cells 

 of the hypocotyl are less sensitive than the cells 

 of the rootlet. If the rootlet is seriously injured, 

 the lack of water supply also affects the hypo- 

 cotyl. Weak irradiations, however, do not 

 affect the water supply of the stem; substances 

 from the stem reach the abnormally slowly 

 growing rootlet; this results in overfeeding the 

 hypocotyl, which accelerates its growth rate at 

 the expense of the rootlet. Consequently, the 

 irradiation of sprouts by weak doses does not 

 always result in growth acceleration, but it is 

 always indicative of the disruption of the balance 

 between the shoot and the rootlet. Bersa con- 

 cludes that X rays are not capable of producing 

 real stimulating effects. 



Beginning in 1928, Johnson began publishing 

 a series of papers dealing with the irradiation 

 of plants, but since her investigations are being 

 continued up to the present [1946], we feel that 

 it would be more appropriate to describe them 

 later. • 



and since the planting took place very late in 

 the season, the control plants never blossomed. 

 The irradiated plants, on the other hand, which 

 had gotten ahead of the controls, bloomed 

 vigorously. Doroshenko's experiments demon- 

 strated the stimulating effect of radiation on the 

 development of reproductive as well as on the 

 vegetative organs of the plants. However, when 

 Doroshenko attempted to increase the exposures 

 (to 20, 30, and 40 minutes), she found that ex- 

 posures of 40 minutes fell beyond the optimum, 

 although still within the threshold of physio- 

 logical stimulation. Still greater exposures 

 (I hour, 1 hour and 15 minutes, and 1 hour and 

 20 minutes), however, already had a retarding 

 effect. The application of a second exposure 

 showed that it had a stronger stimulating effect 

 on development than a single dose. All these 

 favorable data apply to Avena byzantina . The 

 author did not succeed in finding a stimulating 

 dose for Toulouse millet. The same was true 

 for flax (of both the curly and the long-fiber 

 varieties). On the other hand, winter rye not 

 only developed vigorously but also changed its 

 form as a result of irradiation. 



The first experiments with irradiation of 

 potato tubers were performed by Sprague and 

 Lenz in 1929. For their experiments they 

 selected the tubers of two family varieties: 

 "Irish Cobbler" and "Green Mountain. " Half 

 of the tubers were irradiated; the other half 

 were left for controls. The tubers were sub- 

 jected to radiation just after sprouts began to 

 appear. One part (experiment 1) was subjected 

 to doses of 2 HED; the other (experiment 2) was 

 subjected to 1 HED. The first leaves in experi- 

 ment 1 had an abnormal appearance; eventually, 

 however, only normal leaves developed, and 

 they remained green for several days longer 

 than those of the control plants. The yield of 

 the potatoes in number of tubers was 84. 4% of 

 the controls for experiment 1, and 104. 7% for 

 experiment 2. In both irradiated groups, the 

 weight of the average tuber was above average 

 compared to the control. Thus we can see that 

 even heavy irradiation, which injured the leaves 

 and reduced the number of tubers, increased 

 the size of the tubers; therefore, the yield was 

 not diminished. 



Doroshenko (1929) set up experiments with 

 three plants (Avena byzantina , millet, and 

 winter rye). The conditions of irradiation were 

 identical in all experiments, only the length of 

 exposures was varied (5, 10, and 20 minutes). 

 The effects of irradiation became apparent in 

 Avena byzantina from the first stages of devel- 

 opment, especially with the 20-minute exposure. 

 When the plants which had received this dose 

 had already given complete shoots, the controls 

 showed only individual sprouts. In the course 

 of development the stimulating effects became 

 more pronounced: tillering appeared 2 days 

 earlier than in the controls, stems elongated 4 

 days earlier, ears were formed 2 weeks earlier, 



Patten and Wigoder in their experiments in 

 1929 once more returned to the classical objects 

 of roentgenology: the seeds of beans, mustard, 

 and barley. In their opinion, the effect of X 

 rays on growth and development may be studied 

 most easily on plants where cell division takes 

 place so rapidly that the progress of sprouts 

 may be observed daily. Giving the seeds a 

 dose of 3 HED, they observed various reactions 

 which were dependent on the species of plants 

 since other factors were constant. The most 

 sensitive, in their experiments, were the seeds 

 of large beans, especially if they were irradi- 

 ated from 48 to 72 hours after growth had begun. 

 In mustard sprouts the smallest doses (about 



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