CHAPTER 4 



THE EFFECT OF QUANTITY AND QUALITY OF RADIATION 

 ON THE TRANSFORMATION OF PLANTS 



a) Quantity of the radiation. In this chapter 

 we are not going to spend much time in consid- 

 ering the effect of the quantity of X rays on 

 physiological changes, since, actually, all the 

 experiments of this kind indicate a close rela- 

 tionship between the amounts of radiation used 

 and the changes that are produced. If the Arndt- 

 Schultze Law is not confirmed in all cases, it 

 can be ascribed to the fact that the experiments 

 were improperly set up rather than to the nature 

 of the effect itself. 



Here we shall examine those experiments 

 which point to a direct relationship between the 

 dosages and the morphological changes, both 

 hereditary and non -hereditary. Although the 

 results obtained with plants are not as clear 

 as those obtained with the fruit fly [ Drosophila ] , 

 nevertheless there can no longer be any doubt 

 that a direct, linear relationship exists be- 

 tween the dosage and the frequency of mutations. 

 How the frequency of mutations varies in irra- 

 diated corn as dosages are increased can be 

 seen from Table 17. 



Stubbe's article (1933) concerning the rela- 

 tionship between dosage and frequency of gene 

 mutations, after irradiation of male germ cells 

 (which was presented in detail in the second 

 chapter of this book), presents the results of 

 irradiation obtained under three different set 

 ups. These results show a regular rise in the 

 frequency of mutations up to 400 r, after which 

 the frequency falls up to 16,000 r and then rises 

 again. 



In another important experiment, where 

 only the mutations in seedlings were counted, 

 a splendid linear relationship was obtained 

 between doses of 3000 and 6000 r and the num- 

 ber of mutations (Table 33). 



Our experiments in changing the sex of hemp 

 obtained by irradiation with various doses of X 

 rays (see Chapter 2), and Lutkov's experiments 

 with peas and barley (in the same chapter) are 

 good illustrations of this phenomenon [i. e. , 

 the direct relationship between the dose and 

 the effect ] . 



Up to the present time experiments for the 

 purpose of investigating the relationship be- 

 tween the quantity of rays and mutability have 

 indicated that the frequency of mutation is 

 directly proportional to the dosage. 



b) Quality of the Radiation . This question, 

 like the others, has its own history. Way back 

 in 1898, only a year [ 3 years] after Roentgen 

 made his famous discovery, Maldiney and 

 Thouvenin touched on the question of the quality 

 of the rays in their experiments by irradiating 

 seeds of Convolvulus sivensis [arvensis?] and 

 Lepidium sativum with and without filters. In 

 other words, they were trying to determine 

 differences in effect between hard rays (using 

 the filter) and mixed rays. 



Perthes* (1904) on the basis of his experi- 

 ments, came to the conclusion that the intensity 

 of the radiation is more significant than the 

 length of exposure. 



In 1920, KSrnicke in his experiments with 

 Vicia faba did not succeed in establishing any 

 difference in effect between hard and soft rays 

 or filtered and unfiltered ones. 



The experiments of Sierp and Robbers (1923) 

 with the seedlings of oats, whose coleoptyles 

 are most sensitive to rays, confirmed this 

 [i.e., Kornicke's findings] . 



In the same year (1923) Martius set out to 

 determine what biological effects rays of vari- 

 ous wave lengths have when the absorption of 

 energy is kept constant. On the basis of his 

 experiments he came to the conclusion that soft 

 rays have a greater biological effect than hard 

 rays when the absorption of energy is constant 

 and the wave length [ hardness] of the rays is 

 varied. Iven [ 1925] is of the same opinion. 

 Ancel (1928) was the first to experiment with 

 the effects of fractionated doses of X rays on 

 plants, in this case on lentils. In all 18 experi- 

 ments fractionated doses proved to be less 

 harmful than acute doses. Next she [Ancel] set 

 up a very interesting experiment: 18 hours 

 after sprouting, the seedlings of lentils, which 

 had roots 6 millimeters long, were divided into 



97 



