others. TTie author concludes her article with 

 the statement that although the reasons for the 

 resistance or sensitivity of definite species are 

 not known, nevertheless observations of many 

 species establish the fact that the members of 

 certain families (Chenopodiaceae, Portulacaceae 

 and Brassicaceae) are in general resistant, 

 whereas members of other families (Solanaceae, 

 Scrophulariaceae and Carduaceae) are injured 

 more readily than most. 



Nadson [1934] in his article, "At the Inter- 

 national Radiological Congress, " describes an 

 interesting report by two French scientists 

 Golvain [?] and Lacassagne on possible expla- 

 nations of the "individual" sensitivity of organ- 

 isms, i. e. , why two individuals of the same 

 species, which exist apparently, under com- 

 pletely identical conditions, react unequally to 

 some external factor, as, for example, the 

 action of visible or invisible radiation. On the 

 basis of their experiments they propose the 

 following explanation: cells have a certain 

 sensitive zone; the fate of the cells (and, with 

 them, of the whole organism) depends on what 

 kind and how many quanta of radiant energy 

 reach this sensitive zone; this happens to vary 

 with individuals. 



Lambert (1933) set up a series of important 

 and detailed experiments for the purpose of 

 finding out the relationship between the physio- 

 logical condition of the tissues and the sensi- 

 tivity of the plant to X rays. His experiments 

 showed that the boundaries of sensitivity of dry 

 peas lie between 5000 and 10, 000 r; for those 

 which had been soaked in water 6 to 12 hours, 

 not more than 10, 000 r; and for those which had 

 been soaked for 18 to 24 hours, between 2500 

 and 5000 r. Lambert thinks that sensitivity is 

 not a function of the static condition of the seed, 

 which is represented by its chemical composi- 

 tion, but the result of purely dynamic factors 

 introduced by swelling which make the seed 

 sensitive to X rays. 



Gustafsson (1936 [and 1937]) observed a very 

 high sensitivity in cells when they were in meio- 

 sis or in division within the pollen grain, where- 

 as resting seeds were able to take very high 

 doses without losing their ability to germinate. 

 Some authors have concluded from this that the 

 radicle and plumules in the seeds are well pro- 

 tected. However, the pollen mother cells and 

 tetrads are also well protected by the thick 

 tissues of the petals and sepals and by the 

 [anther] wall and tapetal cells, yet they are 

 extremely sensitive to X rays. Accordingly, 

 Gustafsson considers chromosomes in the 

 pollen -mother -cells and tetrads, to be in a 

 more sensitive stage (probably the stage of their 

 reproduction). As for the nuclei of resting 

 seeds, their chromosomes are far from being 

 ready for reproduction and therefore are not 

 sensitive to radiation. In addition, the author 

 attaches great significance to the increase of 



water content in dividing cells. A study of dis- 

 ruptions in nuclear divisions shows that the 

 majority of them are found in nuclei that have 

 just begun division. This demonstrates the 

 differential effect of X rays, on the one hand, 

 and the cytological inequality between the 

 nuclei, on the other. It should be noted that 

 this inequality may depend on the chromosomes 

 themselves. The fact that nuclei may enter 

 into division quickly shows that the chromo- 

 somes are ready for it, but that they are not 

 able to commence without an external stimulus, 

 i. e. , water. According to Gustafsson, the 

 frequency of disruptions of divisions is [directly] 

 related to the water content, and since the 

 nuclei, which are the first to begin division, 

 show the highest frequency in the disruption of 

 this process, the parallel between these two 

 phenomena can only mean that the nuclei, which 

 are the first to divide, contain the greatest 

 amount of water. This assumption is fully con- 

 firmed by the fact that it is possible to change 

 the rate of nuclear division by supplying the 

 seeds with water. 



In their final and exceedingly interesting 

 experiments Stubbe and Doring (1938), suc- 

 ceeded in demonstrating that changes in the 

 physiology of metabolism increase the frequency 

 of mutations. They did so in experiments with 

 malnutrition of snapdragons, the seedlings of 

 which, when grown with insufficient amounts of 

 nitrogen, phosphorus and sulphur, exhibited 

 typical symptoms of starvation. However, 

 plants raised wholly without these nutrients had 

 the same percentage of mutations as the con- 

 trols. It is possible to conclude from this that 

 the deciding factor in mutability is not the lack 

 of nutrients, but disharmony in the metabolism. 

 Further experiments showed that under certain 

 conditions the factor that brings on mutations 

 may, under other conditions (e. g. , a different 

 stage in a plant's development), fail to show up 

 because the transmuted cells may be ejected by 

 the organism or cannot continue their develop- 

 ment due to excessive and severe injury. The 

 authors think it possible that similar processes 

 occurred in other experiments, e.g., those in- 

 volving chemical reactions, thus explaining their 

 frequent failures. Numerous experiments have 

 demonstrated that mutations induced by irradia- 

 tion are determined by the physiological condition 

 of the irradiated object. In order to find out if 

 mineral nutrition affects the frequency of muta- 

 tions in irradiated objects, experiments were set 

 up combining the influence of phosphorus defi - 

 ciency and X rays, i.e., pollen grains both from 

 normal plants and from plants raised without 

 sufficient phosphorus were irradiated. The ex- 

 periments showed that a shortage of phosphorus 

 did not by itself raise the percentage of muta- 

 tions. However, it did so in conjunction with the 

 action of X rays (6000 r) as maybe seen in the 

 much higher number of mutations (Table 37). 



So we see that changes in diet affect not only 



105 



