1. Dormant seeds of Triticum monococcum L. var. vulgare Körn. were exposed to unfiltered X-ray irradiation, which was applied at 90 KVP, 3mA tube current and 15 cm distance for 12.5 to 62.5 minutes. The doses ranged from 2, 700 to 13, 500r units. The frequency of chromosome aberrations (mostly reciprocal translocation) in the P.M.C.'s increased in a parabolic relation to the dose (Table 1). The relatively small increase of the frequency at high doses is assumed to be partly due to limitations ascribed to the “saturation effect”. 2. At equal dose and target distance, with the increase of wave lengths of X-rays obtained by varying the kilovoltage and the time of exposure the aberration frequency decreases (Table 2). 3. If the two-hit aberrations are dependent upon two separate breaks, their new recombination is limited in time and space. The effect of varying the wave length was studied by keeping the dosage and the time of exposure constant and varying the target distance (Table 3). The result was a similar tendency in the relation of frequecy to wave length. 4. These facts could be explained on the basis of a difference in ionization distribution within the nuclei and chromosomes. In the case of hard X-rays much of the total ionization formed by the resulting electrons occurs relatively scattered in their tracks, whereas the ion pairs from soft X-rays are more closely spaced. Since at hard X-radiation chromosome breaks induced by the ionization are scattered in one chromosome or different chromosomes, the reunion of different broken ends, or interchange, occurs more easily than at short radiation with closely adjacent breaks, accompanied by much restitution. 5. In the induced chromosome aberrations in T. monococcum mostly (4)+5II, often 6II+2I and seldom (4)+1IV+3II or (6)+4II were observed, while in tetraploid plants losses of a whole chromosome and deficiencies or duplications of chromosome pieces were found, besides translocations. These results are attributed to the indispensability of at least one complete genome in haplo- and two complete genomes in diplophase, to secure viability in both phases. 6. By fast neutrons and γ-rays were such chromosome aberrations induced like those by X-radiation. The relation of aberration frequency to dose at these exposures was reported preliminary.
1. The association of chromosomes in the spermatogonium and the diploid and the pentaploid nuclei in the second spermatocytes in Oxya vicina Brunner von Wattenwyl in nature has been examined. 2. The chromosomes in metaphase can associate with each chromosome not only with the homologous mates but also with the analogous ones at random. 3. The diploid and the pentaploid nuclei in the second spermatocytes have been observed. 4. These abnormalities as stated above are caused mainly not by the external effects but by the internal forces having some relation with water in the cells.
Chromosome I of Secale cereale has been added to the full cytological complement of Triticum vulgare in several separate fractions, -as the bivalent, as the univalent as the telocentric long arm, as the telocentric short arm, as the isochromosome involving the short arm, and as the isochromosome involving the long arm. All the detectable phenotypic of the effects chromosome seemed to be assignable to the long arm.
The microstructure of the salivary chromosome of Drosophila virilis has been investigated by means of the electron microscope. Flemming's mixture has been used for fixing, and the replica-shadow casting method employed. Thus the most minute structure of the chromosome has been elucidated. 1. The interchromatin regions are composed of a multitude of longitudinal strands, namely, chromonemata. These show beaded struc-ture with a periodicity between 30mμ and 60mμ. 2. The chromomeres distinctly appear when the chromosome has been subjected to digestion with desoxyribonuclease or trichloracetic acid. 3. The matrix is often removed from the chromosomes; but under favorable circumstances it can be observed along with the chromone-mata.
On the bases of a series of studies on karyotypes, chromosome pairing and external characters, the genomic constitutions of all the Japanese members of the genus Trillium were suggested as follows: Plant Chromosome Genom number pairing T. kamtschaticum 2x=10 5II K1K1 T. Hagae 3x=15 5II+5I K1K2T T. Hagae 6x=30 15II K1K1K2K2TT T. Tschonoskii 4x=20 10II K2K2TT T. Smallii 4x=20 10II SSxx T. ainabile 6x=30 15II KKSSxx In the above tabulation, x represents a genom undefined as yet. K1 and K2 are genoms highly homologous, but not identical, at least, chromosome morphologically. These two genoms are comprised by an collective symbol K, when the distinction between them is not necessary in description or is not definitive in the present status of investigation. The writer wishes to express his gratitude to Professor H. Matsuura of Hokkaido University for his valuable suggestions in the course of the work. Expense of the present work was partly defrayed by a Grant in Aid for Fundamental Scientific Research of the Ministry of Education.
The localization of depolymerized and highly-polymerized DNA and RNA in the chloroplasts of some higher plants was demonstrated, using cytochemical methods with methyl green and pyronin and Feulgen's reaction, combined with ribonuclease digestion. The methods of the extraction of nucleic acids from the sectioned materials with trichloracetic and perchloric acids were also employed. The author is indebted to Dr. T. Hama for valuable suggestions and advice during the course of this work and also wishes to express gratitude to Profs. Y. Mori and T. Miduno, Biological Laboratory, Keio University, for their generous help with the experiments.