was increased. A dose of 2500 r had a lethal 

 effect on the pollen. The number of developing 

 seeds in the pods was sharply cut down as the 

 dosages of X rays were increased. Whereas a 

 dose of 300 r gave from 4 to 6 seeds per pod, a 

 dose of 1200 r cut this number down to 1 or 2. 

 Very frequently, despite the development of the 

 fruit [i. e. , the pods], there would be no seeds 

 inside. In Xi only 490 plants grew up, which 

 differed from one another in the power of their 

 development and in morphological changes. 

 Cytological examination of the number of somatic 

 chromosomes in X 2 plants revealed, in one 

 family, the appearance of trisomic forms with 

 15 chromosomes. The additional chromosome 

 induces sharp morphological changes. Thus, 

 one plant was distinguished by very thin trailing 

 stems, by characteristically thin and wide, very 

 large and stretched-out stipules with smooth 

 edges. The leaf blades also had an elongated 

 form, the peduncles were thin, the flowers were 

 smaller than normal ones with a somewhat 

 underdeveloped and narrowed banner. This tri- 

 somic plant, 60% of whose pollen was abortive, 

 turned out to be completely sterile under self- 

 pollination. Another trisomic plant had rough, 

 leathery leaf blades, with a shortening of the 

 internodes, and was partially fertile. A third 

 trisomic plant stood out sharply first by its 

 variegated leaves and by a diminution of the leaf 

 blades. It was completely infertile. In addition, 

 a tetrasomic form turned up in one of the de- 

 scendants of a partially sterile plant from a seed 

 of X3. It had 16 chromosomes instead of 14 and 

 was entirely sterile. 



As for gene mutations, Lutkov found only two 

 instances of chlorophyllic changes: an albino 

 and one with a golden yellow leaf color. Muta- 

 tions of the fasciative type were more frequent. 

 This type of mutational change (which along with 

 the fasciation of the stem, induces stemminess 

 in the plant with distribution of the flowers near 

 the top in the form of an irregular umbrella) is 

 definitely of interest from the agricultural point 

 of view. 



In connection with the second subject of his 

 experiments with X rays (i.e. , barley — 1937*), 

 Lutkov used doses of 400, 600, 800, 1000, 1200, 

 and 1400 r. A total of 876 sprouts were irradi- 

 ated. It became apparent that doses of 1200 r 

 were sublethal and that stronger doses (1400 and 

 1600 r) caused all the plants to die in the initial 

 stages of development. In studying Xg several 

 chlorophyll mutations and an interesting form of 

 barley that lacked ligules were found. Since the 

 plants without ligules appeared among the de- 

 scendants of a single ear, which produced only 

 four seeds (another ear, however, produced 

 plants all of which had ligules), Lutkov assumed 

 that in the given instance, as a result of X radi- 

 ation, a somatic mutation had occurred in one 

 of the cells that produced the single ear and 

 stem. Final confirmation of the nature of the 

 mutation of this plant was obtained from X 3 . 



This form of barley without ligules turned out 

 to be stable and produced only liguleless plants 

 inX3. 



In another experiment (1937*) the author used 

 as his source material the Abyssinian barley 

 Hordeum distichum var. Stendeli KOrn. , a typi- 

 cal spring plant. The plants were irradiated at 

 the stage of ear formation, at a time when the 

 already formed pollen grains were maturing. 

 Doses of 500, 1000, 1500, 2000, and 2500 r 

 were used. The 2500 r dose was the maximum 

 sublethal dose. Analysis of 7, 355 plants from 

 X2, which represented the descendants of 213 

 plants in Xj (besides a whole series of chloro- 

 phyll mutations of the albino, pale cream, yellow, 

 and variegated types), produced a form of winter 

 barley. These plants, which had been left out 

 to vegetate under field conditions until the middle 

 of September and afterwards transferred to a 

 greenhouse, retained their winter type, and con- 

 tinued to bush out. An anatomic examination of 

 the growing points showed that the vegetative 

 cone in these mutational forms of barley is of a 

 characteristic winter type, i.e., the vegetative 

 cone has only the embryonic differentiation of 

 leaves , but no differentiation of embryonic 

 flowers. Consequently, both by their general 

 habits and by their anatomical structure these 

 winter type plants must be considered to be true 

 winter forms of barley. The character of the 

 segregation in Xg, and also in X3 and X4 , of 

 the heterozygous seeds indicates that this par- 

 ticular mutation is a recessive one, apparently 

 produced by a transformation of gene S (spring 

 type) into gene s^ (winter type). 



In a third experiment (1937*), sprouts, dry 

 seeds, and ears were exposed to X radiation. 

 Analysis of Xj of this experiment shows that the 

 basic type of deviations was the narrow -leafed 

 form of the plants, which varied greatly depend- 

 ing on the stage of its development. Side by 

 side with almost needle-like forms it was possi- 

 ble to observe plants with insignificant devia- 

 tions from the control. The narrow -leafed 

 forms had low viability and complete sterility. 

 A very small number of these plants reached 

 the stage of ear formation; these ears, it should 

 be noted, had nothing in common with the 

 double -row type of ear from which they are 

 derived, rather they remind one of Aegilops . 

 Other types of "radiomorphs" were two-eared 

 forms with cylindrical ears (with a development 

 of additional bracts at the base of the ear), then 

 plants with a more compact type of ear, plants 

 with less compact types of ears, etc. Analysis 

 of subsequent generations demonstrated that all 

 the types of "radiomorphs" enumerated above 

 are not hereditary deviations and in Xg produce 

 normal -looking plants. However, an analysis 

 of X2 revealed many gene mutations of the re- 

 cessive type, which arose as a consequence of 

 X radiation and which were found in X 1 in a 

 heterozygous condition. The bulk of these 

 changes consisted of various chlorophyll 



42 



