55%, "Ukrainka" -51%, "Saratovskaya" -39%, 

 "Odesskaya Girka" - 17%, "Kooperatorka" - 16%, 

 "Stepnyachka" -12%. These experiments permit 

 the author to conclude that with the aid of X radia- 

 tion it is possible to obtain a greater or lesser 

 variety of chromosomal aberrations, chiefly 

 sterile ones, and a smaller number of gene mu- 

 tations, which retain their changes in future 

 generations. From this, the selective signifi- 

 cance of this new method of creating new forms 

 can be seen. From X3 of winter wheat "Koope- 

 ratorka" a frost -resistant X-ray mutation was 

 obtained. 



Chekhov in 1930* irradiated dry seeds of 

 barley, lentils, wheat, and rye. By means of 

 very thorough daily observations he was in a 

 position not only to determine the stimulating or 

 depressing effects of X rays, but also to detect 

 the mutations arising in the early stages of de- 

 velopment. Despite larger doses of X rays than 

 those used by Stadler, Chekhov obtained only six 

 X-ray mutants from barley. One of these, as a 

 seedling, had leaves with a yellow tint, which in 

 time became still more yellow, and, finally, 

 died. Four were typical albinos; they also died. 

 The sixth plant had at the beginning of its devel- 

 opment leaves completely devoid of chlorophyll. 

 Part of them never turned green and wilted away; 

 the other part turned green after several days, 

 but the green coloring did not develop evenly: in 

 some cases it developed from the tip of the leaf 

 towards the sheath, covering the entire blade of 

 the leaf; in other cases it proceeded from the 

 sheath towards the tip of the leaf; occasionally 

 the green coloring appeared in isolated areas in 

 the center of the leaf in the form of tongues, or 

 else only the veins turned green. 



When all of the X-rayed barley seeds were 

 planted at the zonal seed station, only four speci- 

 mens were found with chlorophyll deficiencies. 



Among the collected plants grown from X- 

 rayed seeds, Chekhov observed in the barley 

 "Chervonets" the following X-ray variations: 

 1) low growing forms, 2) changes in the distri- 

 bution of rows in the ears, 3) more frequent 

 occurrences of naked seeds in the ears. 



In the winter wheat "Durable" he observed: 

 1) low growing forms, 2) sturdier and looser 

 ears, 3) a bluish coloring of the ears. 



The rye "Vyatka" produced: 1) low growing 

 forms, 2) changes in compactness and form of 

 ears, 3) ramose ears. 



After irradiating lentil seeds, Chekhov ob- 

 served two albinos, which at first developed on 

 a par with the controls, but eventually died. 



The experiments which Delone has been con- 

 ducting since 1928 occupy a special place in the 

 field of genetic effects of X rays. We have 

 singled out these experiments not only because 



they were performed with wheat, which is the 

 most important crop for the USSR (in itself a 

 very important fact), but chiefly because they 

 have demonstrated how powerful a factor X rays 

 can be in creating new biological forms. The 

 X-ray mutations obtained by Delone were com- 

 plex in their phenotypical aspect. Delone sees 

 the explanation for this not only in the pleio- 

 tropic action of individual genes, but also in the 

 fact that the changes to mutations simultaneously 

 affect whole bundles of genes, as a result of the 

 aberration of the chromosomes. Delone in his 

 experiments regards as gene mutations only 

 certain bearded mutants, those with naked ears, 

 and probably the squarehead; other X-ray mu- 

 tants are chromosomal aberrants. The pro- 

 fundity of the changes is such that taxonomists 

 would not attribute certain of the mutants to the 

 species from which they were derived. 



The variety and profundity of the transforma- 

 tions Delone obtained in his experiment pre- 

 sented a picture that recalls the development of 

 new forms observable in the descendants of 

 hybrids between distant species. The variety 

 of directions taken by the mutations was so 

 great that among the 64 X-ray mutants very 

 few similar forms are found. In his presenta- 

 tion Delone examines the transformations by 

 individual characteristics. 1) Compactness of 

 ear. In the variety "Delphi" used by Delone, the 

 compactness of the ear was 3. 1, whereas some 

 of the X-ray mutants had a compactness of 4. 4, 

 and others, 1.8. The character of compactness 

 of the ears was very diverse: there were 

 squareheads, "reverse squareheads" [speltoids] 

 "compactoids, " and evenly compact ones with 

 long ears. 2) Size and shape of covering scales . 

 The covering scales vary in length from 5. 5 to 

 10 millimeters; in width, from 2 to 4 milli- 

 meters. In shape, the covering scales are 

 extremely diverse, ranging from blunt and flat 

 scales of speltoids to sharp and pear-shaped 

 ones. 3) and 4) Beardedness and furriness of 

 ears. These features vary greatly, just as 

 does the length of the hairs. In Xg a completely 

 naked X-ray mutant appeared. 5) The waxy 

 layer is developed to different degrees . One 

 X-ray mutant was completely devoid of the waxy 

 layer. 6) Pigmentation of the ears (among the 

 X-ray mutants white-, red-, and black-eared 

 ones could be found). 7) Fertility . On the basis 

 of fertility Delone divides his mutants into four 

 groups: a) completely fertile, b) slightly fertile, 

 c) almost non -fertile, and d) completely non- 

 fertile. 8) Length of growing season . A pro- 

 longed growing season seems characteristic for 

 certain of the mutants. 9) Height of plants . 

 The height of the stalks varies from 8 centi- 

 meters in dwarfs to 79 centimeters. 



The changes due to mutations found expres- 

 sion in all aspects which could be observed 

 without recourse to more refined methods of 

 examination. 



Delone points out the tremendous scope of 



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