The mitotic chromosomes of Drosophila virilis observed in the oesophageal ganglion cells are longitudinally differentiated as regards the structure into two kinds of chromatin-heterochromatin and euchromatin. The proximal halves of chromosomes adjacent to the spindle attachment regions which are composed of heterochromatin remain chromatic and fail to disintegrate during the interphase, while the distal halves consist of euchromatin, with the exception of the Y chromosome which is totally heteropycnotic. Observations made through the mitotic cycle showed that it is those heterochromatic regions which fuse, including the Y chromosome, to form the chromocentre right through the telophase to prophase. Some remarks on the relation between the chromocentre of the salivary gland nucleus and that of the mitotic nucleus are given.
1. The sixth salivary gland chromosome of the New Orleans strain of D. virilis has a markedly lower staining capacity than that of other strains. 2. This chromosome is also wider and longer than those in other strains. The arrangements of the bands, however, show no difference when crossed, a complete somatic synapsis occurs between this chromosome and the corresponding chromosome of any other strains in the heterozygous condition. 3. Among 23 strains from various localities of Japan and China, as well as of America examined, none had a sixth chromosome like that of the New Orleans. Only a mutant stock, Gap2 hump/lethal 6a derived from the American Gap2 stock, contained such a chromosome. 4. No difference was found in the frequency of crossing over between the sixth chromosomes of the New Orleans and that of other strains. 5. In a new composite chromosome derived from such crossing over, the distal half from VI1A to VI1G is made up of the New Orleans chromosome and the other half of a section, VI1F to the proximal end, of a normal chromosome. This gives another case of cytological demonstration of the phenomenon of crossing over. 6. A new allelomorph of Gap11 was discovered in the New Orleans stock. 7. No significant difference in genetical behaviour exists between the New Orleans and normal strains. Nevertheless the markedly low viability and fertility of the stock with the recombination sixth chromosome is possibly due to some incompatibility between the two kinds of chromosomes.
1. When the epidemis cell of Allium cepa is plasmolysed with a 0, 5 mol KCl solution, concave plasmolysis continues longer than hitherto expected, if the material is preserved in healthy condition and its treatment during the experiment is carried out carefully. 2. When KCl is used as the plasmolyticum, the difference of the material and the experimental condition react more sensitively in the plasmolysis form and time than when CaCl2, or saccharose is used. 3. Judging from the plasmolysis form the liquefying action of K. on the cytoplasm increases accompanied by the increase of hydrogen ion concentration. 4. Light has remarkable influence on the plasmolysis form and time. The plasmolysis time is shortened by illumination of the preparation. This is theoretically in accordance with the well-known fact that the light increases the permeability of the protoplasm. 5. In order to have uniform healthy material of Allium cepa for the purpose of the experiment on the plasmolysis form, it may be recommended that the bulb or the separated scale leaf be kept cool and wet, or better in cool water. This was confirmed by repeated experiments in the present investigation. 6. Ca.. and A1.. act antagonistically against K. in relation to the plasmolysis form. The plasmolysis time is greatly prolonged by the addition of these ions. A part of the present study has been carried out at the Laboratory of Plant Physiology of Prof. T. Sakamura, Sapporo, to whom the writer wishes to acknowledge his sincere gratitude for granting him the facilities of the laboratory. The writer expresses his thanks equally to the Japan Society for the Advancement of Cytology, by the grant from which this work was supported.
The maturation division and pollen development of Scirpus lacustris L. var. typicus Honda have been described. Typicus has two compound chromosomes in diploid which pair quite normally in meiosis. In the I-telophase this compound chromosome pair forms very often chromosome bridge which always have a sagittate form showing clearly more than one fibre attachment. The compound chromosome found in typicus is different from that found in the animal kingdom in two points, i.e. firstly, it shows the compound feature throughout the life cycle, and secondly, it gives clear direct evidence for the compound feature showing more than one fibre attachment in the bridge formation. Thus the previous prediction that the compound chromosomes first found in typicus and then found in pictus may be equivalent to three small chromosomes, is to some extent fulfilled. Quartet nuclei are of the same size when they are first formed and then move together inwards of the PMC, but soon one of them which is situated in the outer-most position of the PMC grows larger and the rest are pushed to an inner corner of the PMC. In the interstage of the prophase and metaphase of the primary pollen nuclear division, a septum is formed between the pollen nucleus and the three small nuclei which finally degenerate, and at the same time or somewhat later, septa are also formed among the three small nuclei. The three small nuclei proved to possess the ability of dividing by themselves. A pollen nucleus undergoes mitosis in the normal way to give rise a generative nucleus inwards and a vegetative one outwards. A generative cell plate is formed by means of the union of the phragmoplasts which appear at first in the center of the telophasic spindle of the primary pollen nuclear division. It is, at first, situated along the wall which divides the pollen nuclei and the micronuclei in the corner. Between the daughter nuclei in the corner which have arisen by the nuclear division of the three small nuclei no septum has been formed, and finally they fuse two by two which are at last pushed against the cell wall to die. The septa formed in an inner corner of the PMC seem finally to destroy. Here the writer wishes to express his best thanks to Prof. Y. Sinotô, by whose suggestion these studies were started, for his valuable advice throughout the course of the work.
1. Verschiedenartige Pufferlösungen von pH 4, 0-9, 0 bei der Konzentration von 0, 001-0, 05 GM bedingen verschiedene Strukturanomalien von Chloroplasten und Zytoplasma. 2. Diese schädliche Wirkung der Salzlösungen, an der neben H- und OH-Ionen auch Anionen wesentlich teilnehmen, läßt sich durch Ca- und Mg-Ionen in verschiedenen Maßen vermindern (Entgiftung). 3. Relative Wirksamkeit der verschiedenen Pufferlösungen von demselben pH geht mit der quellenden Wirkung auf Gelatinegallerte in Parallele. Dabei macht Phthalat-Puffer eine Ausnahme. 4. Es hat sich wenigstens bei Phosphat- sowie Zitrat-Pufferlösungen gezeigt, daß die Anionen in den Pufferlösungen der quellenden Wirkung von OH-Ionen anscheinend entgegenwirken, so daß die höhere Konzentration der Pufferlösung gleichsam wie die Erniedri gung des pH derselben wirkt (vgl. YAMAHA u. ISHII 1932). 5. Sulfat-Ionen machen Spirogyra-Zellen schwer plasmolysierbar und bedingen Chloroplastenkontraktion. Zum Schluß möchten wir der Japanischen Gesellschaft zur Förderung der Zytologie für ihre finanzielle Unterstützung an dieser Untersuchungen unseren aufrichtigsten Dank aussprechen.
1) Through the subjection of Trillium plants to high temperature (20°C) prior to the meiotic divisions, several abnormal types of division were obtained in their PMCs. They were classified into (1) mitotic, (2) supra-mitotic and (3) ultra-mitotic. These are diagrammatically illustrated in Fig. 1. 2) In the mitotic type the 10 separate univalents (dyad chromosomes) appear at metaphase instead of the 5 bivalents. The supra-mitotic type is characterized by the formation of the 20 separate chromatids, and the ultra-mitotic type by the 40 separate half-chromatids. The occurrence of the last type indicates that the chromosome at meiotic prohase consists of at least four separable chromonemata. 3) In the meiotic and mitotic types, there appeared corresponding “precocious” types, in which the kinetochores have already split further at metaphase and each chromosome consists of two separate chromatids lying parallel within the pellicle and coiling independently. 4) It was demonstrated that meiosis is convertible through acceleration of cell activity into mitosis, not only in the behavior of chromosomes but also in their structure. This implies that meiosis differs in its mechanism from mitosis in the retardation of prophase, not in precocious chromosome development as Darlington assumes.
1) The paired chromatids of each meiotic chromosome constitute at early metaphase the relational spiral system (Fig. 1A), while those at late metaphase take the parallel system (Fig. 1B). 2) This conversion of the spiral system takes place first from the proximal region and then independently from the distal end. These processes proceed inwards along the arm and when they meet one another the parallelisation is completed. 3) Such an orientation of the parallelisation excludes a possibility that the system is altered by rotation of the free end. The other possibility must, therefore, be admitted that the parallelisation is associated with breaks and reunions between the chromatids at twisting points existing in the spiral system. This breakage is supposed to be caused by the cleavage of the matrix enveloping the minor spiral, which at the same time plays a rôle for preventing the transversal reunions of the broken ends (Fig. 26). 4) According to the writer's Neo-two-plane theory, the paired chromatids are non-sisters in two-thirds of the Gases. Therefore in these cases such breaks and reunions should result in detectable crossovers. 5) This new hypothesis of crossing-over mechanism presents reasonable expianations for many essential characteristics hitherto known in the crossing-over phenomena.
Three different effects (the primary, mitosis-free period and the secondary effects) of neutron bombardment on the root-tips of Vicia faba were described cytologically. The primary effect consists of advancement of the mitotic process from metaphase to telophase, retardation of the same mitotic process owing to the chromosome aberration and relative advancement of chromosome formation from prophase chromonemata. The former may chiefly be attributed to the effect on the cytosome and chromosome (dehydration) which resulted in an increase in the number of mitotic figures in the telophase, while the latter two are attributed to the effect an the chromosomes, namely fragmentation, clumping and hydration. These, moreover, result in an accumulation of mitotic figures in the metaphase and later stages. The mitosis-free period results from the delay in chromosome formation from the resting nuclei, induced after irradiation. The secondary effect, which reveals itself after the mitosis-free period, shows abnormalities appearing in the process of recovery of cells from the effect of the neutron bombardment. Fragmentation and fusion of the chromosomes and irregular mitoses were observed 96 hours after irradiation. The fragments formed were chiefly chromosome fragments and rarely chromatid fragments. The abnormal changes in somatic mitoses produced by the action of neutron rays may be comparable with those seen in the case of the desiccation treatment (cf. Wada 1936). These investigations were carried out according to the program of the Atomic Nucleus Sub-Committee of the Japan Society for the Promotion of Scientific Research to which we wish to express our gratitude. We are indebted to the Japan Wireless Telegraph Company for the electromagnet and other pieces of equipment used for the cyclotron, and to the Mitsui Hoonkwai Foundation, the Tokyo Electric Light Company, and Mr. G. Hattori, Director of K. Hattori Company, for financial aid. We acknowledge the kind assistances given by our colleges of the Nuclear Research Laboratory in connexion with the irradiation of samples.