Table 20 

 (based on Lutkov's data, 1937*) 



deviations. The frequency of mutations in- 

 creased with increase of dosage (Table 20). 



TTie percentage of mutations was determined 

 by the ratio of the number of plants that are 

 heterozygous due to mutational changes of ears 

 in Xj to the total number of ears examined for 

 each dosage, the hereditary character of the 

 changes being checked in Xj. 



The basic type of chlorophyll mutations of 

 the shoots are mutations of the "albino" type. 

 These are shoots devoid of chlorophyll develop- 

 ing 2 to 3 leaves and then dying on the twelfth to 

 fifteenth day of their development. Then follow 

 mutations of the virens type (white -yellow, 

 yellow -green, and pale yellow mutations) char- 

 acterized by lateral and longitudinal stripings of 

 the leaves, etc. These are all chlorophyll devi- 

 ations appearing in Xg in a homozygous condition 

 and are recessive mutational changes of a lethal 

 type. An exception is formed by a single type, 

 which is characterized by a longitudinal striping 

 of the leaves. This feature varies with the dif- 

 ferent stages of development of the plant. At 

 the beginning of the growing season these muta- 

 tional forms look like perfectly normal green 

 plants. On the twentieth to twenty-fifth day 

 white stripes begin to appear on the newly ap- 

 pearing leaves. These stripes are narrow at 

 first, but gradually embrace greater and greater 

 areas of the leaf blades. Finally, almost com- 

 pletely white leaves appear and only a small part 

 of these mutational forms ever reach the stage 

 of ear formation. The character of the segrega- 

 tion of the phenotypically normal plants of Xj 

 indicates that this mutation is of a recessive 

 type. 



In addition to the chlorophyll, liguleless, and 

 winter types of barley mutational changes, X 

 radiation of dry seeds produced hereditary 

 changes of ears resembling the ears of Hordeum 

 intermedium . The ears of this mutational form 

 exhibited branching, forming at the base of the 

 ear branch ears which were somewhat deformed 

 in appearance. The number of grains in the 



ramose form of barley in some cases reached 

 25 to 28, whereas in the double -row ears of 

 Hordeum distichum var. Stendeli the number of 

 grains varies from 18 to 22. This mutational 

 form remained stable even in X4. The charac- 

 ter of the segregation indicates that the given 

 mutation is a recessive mutation of a single 

 gene. Still more singular was the mutation 

 which resulted in the almost complete deforma- 

 tion of the ear. It was characterized by under- 

 development of the individual little ears along 

 the length of the ear, by the absence of flower 

 membranes, ovaries, and anthers, and by dis- 

 tortion of the axis of the ear. When individual 

 seeds of this mutational form were planted, it 

 proved to be completely stable in X3. 



In addition to all the above mutations, five 

 dwarfs were found in X2. They proved to be 

 stable and fertile. 



Young (1940) observed the occurrence of a new 

 mutation from irradiated tomato seeds. This 

 new character remained constant for two genera- 

 tions. Apparently, the mutation was homozygous. 

 When the new X -ray mutant was crossed with 

 normal plants possessing yellow -colored corol- 

 las, the latter dominated in Fi, and a typical 

 monohybrid segregation was observed in F2. 



Gustafsson and Aberg (1940) obtained two 

 mutations by irradiating seeds of a pure strain 

 of barley "GuUkorn. " These mutations (one of 

 them a double -flowered mutation, the other with 

 changed scales) are interesting from a selective 

 point of view since they indicate that it is possi- 

 ble to obtain mutations that go beyond the limits 

 of normal variability in cultivated and high 

 yielding crops. 



We turn now to a description of the works of 

 Stubbe who investigated the effects of short wave 

 [ionizing] radiation on plants continuously from 

 1927 [?] to 1940. The first work was taken up 

 with the purpose of supplementing Baur's inves- 

 tigations (which were begun in 1927) on obtaining 

 mutations experimentally. As source material 

 he used the descendants of the same strain (A50) 

 of snapdragons that had been used by Baur. This 



43 



