chromosomes, which results in their fusion, 

 fragmentation and other similar disorganizations 

 in the nucleus and its contents. In nuclei that 

 have received such doses one can clearly observe 

 from metaphase to telophase pycnosis or con- 

 traction of the chromosomes into a darkly stained 

 mass. This can be observed in meiosis as well 

 as in mitosis. KOrnicke, Komuro, Marshak, 

 Pekarek, Stone, and Husted all observed this 

 phenomenon. Pycnosis may be preceded by a 

 shortening and a thickening of the chromosomes 

 prior to metaphase (Riley [1936]) and breaks in 

 the prophase threads (Sizova [1936]). 



Less drastic, but equally lethal or sublethal 

 effects, are described in detail by various inves- 

 tigators. The induced changes include: extreme- 

 ly aberrant and irregularly distributed chromo- 

 somes, reconstructed nuclei, cells with micro- 

 nuclei, multinuclear cells, chromatin plates 

 [bridges] between two or more daughter cells, 

 the formation of two or three spindles, etc. 

 Increases in the number and size of nucleoli, 

 their vacuolization and improper budding almost 

 always accompany such nuclear changes. 



All of these changes were observed by the 

 following investigators: Delone, Goodspeed, 

 Avery, 20 Olson, 20 Huskins and Hunter, Husted, 

 Katayama, KOrnicke, Komuro, KraevoT, Levit- 

 skii, Araratyan,20 Shepeleva20 and Titova,20 

 Sizova, Marshak, Bolman,20 Mather, McClint- 

 ock, Metz, Mol, Nadson, Rokhlina,20 \4_ Nava- 

 shin, Nebel, Noethling and Stubbe, Patten and 

 Wigoder, Pekarek, Riley, Sax, Stone, Strange- 

 ways and Hopwood, Ternovskii, Thompson,* 

 jUngling,20 and Langendorf.* 



By means of X rays, questions concerning the 

 mechanism of chromosomal rearrangements and 

 the condition of chromosomes at various stages 

 in the nuclear cycle have also been studied. On 

 the basis of numerous investigations of plant and 

 animal organisms subjected to the action of 

 X rays, it is possible to regard as established 

 the fact that chromosomal changes are due to 

 the direct action of X rays, and not to the influ- 

 ence of cytoplasmic changes. 



In addition to these changes, Komuro [1922- 

 1928], and Patten and Wigoder [1930], observed 

 multinuclear cells in Vicia ; and Huskins [and 

 Hunter (1935)], in Trillium. 



Cytological Investigations Performed 

 in the Electrobiological Laboratory 



In the first part of our work we presented 

 data on physiological changes in rye, peas, and 

 wheat, and on the increase in yield of the first 

 two. In our cytological investigations we 



^Collaborators. 



uncovered certain regularities which relate 

 these changes to the intracellular ones. 



Rye — Sprouts and Seeds (Investigation by 

 Afanas'eva, Breslavets, and Medvedeva ). After 

 studying the morphology of the resting nucleus 

 and the process of cellular division in normal 

 rye, we proceeded to investigate the nuclear 

 changes due to the action of X rays. With dos- 

 ages of 250 r the most frequent changes ob- 

 served by us were the appearance of cells with 

 two nuclei, whose fate differed, depending on 

 how far apart from each other they were located. 

 If they lie close together, they soon fuse and 

 give rise to tetraploid nuclei. If they lie at 

 some distance from each other, the cell re- 

 mains binucleate for some time. This condi- 

 tion, however, stimulates more rapid division, 

 and cells with single nuclei result. This same 

 dose results in the appearance of a doubled 

 chromosome number and a related increase in 

 nuclear size. In addition to these changes, 

 which cause an increase in the amount of nucle- 

 ar material, which in turn leads to an increase 

 in cellular activity and stimulation of the growth 

 and development of the plant, other changes 

 were observed that cannot be considered to be 

 beneficial to the life of the cells and the develop- 

 ment of the plant. These latter changes consist 

 of a flowing out of the nucleoli from the nuclei 

 and even the flowing out of the nuclear material 

 itself. These changes are encountered at a 

 dose of 250 r so rarely that they do not have 

 much effect on the activity of the cells; they do, 

 however, serve as a warning that it is danger- 

 ous to increase this dosage. In addition, vari- 

 ous irregularities appear at prophase which 

 imitate the figures of reduction-division. The 

 irregularities at prophase lead, as cell division 

 proceeds, to irregularities at metaphase such 

 as fusion of the chromosomes into one or more 

 shapeless globs or sometimes even their com- 

 plete decomposition. With a dose of 250 r these 

 abnormalities are few, but as the dose is in- 

 creased, the number of abnormal figures in both 

 resting and dividing nuclei increases. The num- 

 ber of cells in which the nuclear material is 

 completely disintegrated increases greatly. 

 This phenomenon reaches its maximum fre- 

 quency with a dose of 8000 r. Besides, the 

 number of dividing nuclei decreases, beginning 

 with a dose of 1000 r. With a dose of 4000 r, 

 dividing nuclei are almost never encountered. 

 If we remember (as has been pointed out in the 

 first part of our work which is devoted to physi- 

 ological changes induced by X rays) that all 

 plants which received doses of 4000 and 8000 

 r died, then the reason for their death becomes 

 quite clear. Strong doses of X rays destroy the 

 nuclei, and cells deprived of their nuclei sooner 

 or later die off. Even if the injury to the 

 nucleus is not too great, it still loses its ability 

 to divide, or else divides very slowly. The tips 

 of the roots, not having any other means of 

 increasing in size except by elongation of the 

 cells, at first stop growing and then slowly die. 



77 



