after changes in external conditions. Besides, 

 this hypothesis is bolstered by the fact that from 

 the 18 mutations obtained by irradiation of 400 r, 

 four are obtained many times and only four ap- 

 peared at first. It is obvious that the 400 r dose 

 affects the more labile areas. If we call genes 

 which change frequently, "labile genes," it is 

 clear that with 400 r the percentage of mutations 

 of labile genes reaches 78% and then falls from 

 dose to dose, and that with 3200 r it only equals 

 25%. Conversely, as the dose increases, the 

 percentage of mutations of new genes, which 

 appear for the first time, rises. 



Moreover, in his previous work in 1932 Stubbe 

 established that genes which affect vegetative 

 organs show an increase in the percentage of 

 mutations with each increase of dosage, while 

 genes which determine the shape and color of 

 the flowers do not show any rise in the number 

 of mutations in comparison with non- irradiated 

 plants. From these facts we can conclude that 

 genes which determine the characteristics of 

 generative organs are extremely stable or that 

 the process of mutation is related to various 

 stages of development. 



The results of irradiation of Crepis tectorum 

 obtained by Gerasimova in 1940 are very inter- 

 esting. Mature ovicells were subjected to X 

 radiation. The peripheral flowers were emas- 

 culated and one half hour after irradiation (with 

 2800 r) were fertilized by normal pollen. In 

 1934 from 20 seeds of one inflorescence 8 sterile 

 plants were obtained, 7 had normal chromo- 

 somes, 1 was a translocated one (i. e. , an inter- 

 change of parts of the B and D chromosomes 

 took place). This latter plant was non -fertile 

 under self-pollination, but under free pollination 

 it produced 972 seeds from which (in 1935) 200 

 plants were grown and subjected to analysis. 

 It turned out that these descendants could be 

 divided into three groups: 1) typically normal 

 plants, 2) plants which repeated the conduct and 

 external appearance of the original trisomic 

 plant (based on chromosome B), and 3) under- 

 developed dwarfs. Cytological analysis revealed 

 an extremely interesting phenomenon: the 

 genetic specificity of parts of the chromosome. 

 The distal end of chromosome B disturbs the 

 balance of the genes, creating external effects, 

 whereas the proximal end does not do so. Fur- 

 thermore, it turned out that if, at one of the 

 developmental stages, a partial loss of the distal 

 end of chromosome B occurred in the cells of 

 the vegetative cone, then monstrous, dwarf, 

 and generally abnormal forms would develop. 



Change of Sex Due to Effects of X Rays 



Knapp and Schreiber (1936) irradiated 

 Sphaerocarpus donnellii in three different 

 stages: 1) shortly before reduction-division, 

 2) very young tetrads after reduction -division, 

 and 3) mature spores. They used high dosages 



of X rays (from 1000 to 15, 000 r). The experi- 

 ments showed the differential sensitivity of 

 these stages. The young tetrads shortly after 

 reduction -division turned out to be most sensi- 

 tive, mature spores the least sensitive. As is 

 well known, sex in this moss is determined on a 

 strictly genetic basis. The diploid spore mother 

 cells (with 14 + X -t- Y chromosomes) always 

 develop into 2 female haploid spores (7 + X) and 

 2 male haploid spores (7-1- Y). 



When the control spores are planted, they 

 always produce 50% male and 50% female plants. 

 After irradiation one always observes a pre- 

 dominance of male specimens, which becomes 

 more pronounced as the dose is increased. 

 Analysis of the tetrads shows that this shift is 

 due not only to selectivity, or a greater depres- 

 sion of the viability of the female plants, but 

 also to a transformation of females into males. 

 Cytological examination confirms this premise. 

 If the tetrads had 3 male spores, then two of 

 them had 7 4- Y, and a third had 7 -I- an incom- 

 plete X chromosome or a fragment of it. Ap- 

 parently, that piece of the chromosome which 

 carries the female determinant is lost. The 

 transformed male specimens showed little dif- 

 ference from normal male plants; they had 

 normal anthers. In general, however, they were 

 more robust and they developed more quickly. 

 The authors explained this increase in size of 

 cells and organs as due to the effect of an in- 

 creased amount of chromatin. However, the 

 formation of spermatozoids in the transformed 

 specimens was disrupted. The spermatozoids 

 were feebly motile and sterile. 



Investigations Performed in the 

 Electrobiological Laboratory 



As has already been pointed out in the first 

 part of this book, our experiments were per- 

 formed in a laboratory, which can really be 

 called an electrobiological laboratory that 

 changed its location but retained its purpose 

 and program. The following personnel partici- 

 pated in the work: Atabekova, Afanas'eva, 

 Breslavets, Medvedeva, and Tom. 



Rye. In our experiments with rye among 

 plants whose ears were of normal shape and 

 size we encountered X-ray mutants that differed 

 in this respect. The most obvious ones were 

 with branching ears, then those with short and 

 compact ears (which reminded one of square- 

 head wheat by their shape), then those with tri- 

 florous ears, and also wide and flat ones, 

 spindle-shaped ones, and abnormally thin ones. 

 Consequently, it was possible to obtain by 

 means of X rays several new forms from which 

 a selection could be made. 



The most interesting from an agricultural 

 point of view were two X-ray mutants: 1) with 

 ears of the squarehead type, and 2) with tri- 

 florous ears. 



46 



