Abstract: Individual bivalents or chromosomes have been identified in Drosophila melanogaster spermatocytes at metaphase I, anaphase I, metaphase II and anaphase II in electron micrographs of serial sections. Identification was based on a combination of chromosome volume analysis, bivalent topology, and kinetochore position. — Kinetochore microtubule numbers have been obtained for the identified chromosomes at all four meiotic stages. Average numbers in D. melanogaster are relatively low compared to reported numbers of other higher eukaryotes. There are no differences in kinetochore microtubule numbers within a stage despite a large (approximately tenfold) difference in chromosome volume between the largest and the smallest chromosome. A comparison between the two meiotic metaphases (metaphase I and metaphase II) reveals that metaphase I kinetochores possess twice as many microtubules as metaphase II kinetochores. — Other microtubules in addition to those that end on or penetrate the kinetochore are found in the vicinity of the kinetochore. These microtubules penetrate the chromosome rather than the kinetochore proper and are more numerous at metaphase I than at the other division stages.

Abstract: After lysis in a Brij 58-polyethylene glycol medium, PtK1 cells are permeable to small molecules, such as erythrosin B, and to proteins, such as rhodamine-labeled FAB, myosin subfragment-1, and tubulin. Holes are present in the plasma membrane, and the mitochondria are swollen and distorted, but other membrane-bounded organelles of the lysed cell model are not noticeably altered. After lysis, the mitotic apparatus is functional; chromosomes move poleward and the spindle elongates. Cells lysed while in cytokinesis will continue to divide for several minutes. Addition of crude tubulin extracts, MAP-free tubulin, or taxol to the lysis medium retards anaphase chromosome movements but does not affect cleavage. On the other hand, N-ethylmaleimide-modified myosin subfragment-1, phalloidin, and cytochalasin B inhibit cleavage but have no effect on anaphase chromosome movements under identical lysis conditions. These results suggest that actomyosin plays no functional role in anaphase chromosome movement in mammalian tissue culture cells and that microtubule depolymerization is a rate-limiting step for chromosome-to-pole movements.

Abstract: Mitotic chromosomes from human peripheral lymphocytes studied at the junction of metaphase and anaphase show that the centromeres of various chromosomes separate in a nonrandom, apparently genetically controlled sequence. It does not depend upon the position of the centromere in the chromosome, the length of the chromosome or total amount of detectable C-chromatin. In man, several chromosomes e.g. 18, 17, 2, separate very early. Such “early” cells do not include nos. 1, 13, 14, 15, and Y and very rarely nos. 21 and 22. The last separating chromosomes are those from group D, G, no. 1, 16, and Y. The possible implication of these findings in evolution, non-disjunction and the control of centromere separation sequences is discussed.

Abstract: The interphase nucleus in theFunaria caulonema tip cells is associated with many non-cortical microtubules (Mts). In prophase, the cortical Mts disappear in the nuclear region; in contrast to moss leaflets, a preprophase band of Mts is not formed in the caulonema. The Mts of the early spindle are associated with the fragments of the nuclear envelope. Remnants of the nucleolus remain in the form of granular bodies till interphase. The metaphase chromosomes have distinct kinetochores; the kinetochore Mts are intermingled with non-kinetochore Mts running closely along the chromatin. Each kinetochore is associated with an ER cisterna. ER cisternae also accompany the spindle fibers in metaphase and anaphase. In telophase, Golgi vesicles accumulate in the periphery of the developing cell plate where no Mts are found. The reorientation of the cell plate into an oblique position can be inhibited by colchicine. It is concluded that the ER participates in controlling the Mt system, perhaps via calcium ions (membrane-bound calcium ions have been visualized by staining with chlorotetracycline) but that, on the other hand, the Mt system also influences the distribution of the ER. The occurrence and function of the preprophase band of Mts is discussed.

Abstract: Premature chromosome condensation (PCC) was induced in order to study the arrangement of muntjac chromosomes in the interphase nuclei of proliferating and resting cells with respect to their polarity and the spatial relationship between them. The data were compared with the situation in in situ fixed and colcemid blocked metaphases. It appears that in rapidly dividing cells almost all G1- and G2 interphase chromosomes exhibit the Rabl type polarized orientation. This pattern still predominates in G0 lymphocytes which may have been arrested at this stage for some months or even years. — The location of the small chromosome Y2 was found to be “central” in normal metaphases but “peripheral” in colcemid blocked mitoses. The behavior in the premature condensed chromosome preparations was intermediate. Measurements of centromere distances between all possible pairs of chromosomes as well as on the relative position of chromosomes in circular spreads revealed no evidence for homologous somatic association during interphase and metaphase or any other suprachromosomal ordering principle. Interphase chromosome orientation seems to be solely the result of chromosome arrangement of the foregoing anaphase. Association between heterochromatic regions or the nucleolus organizers did not substantially influence this pattern. There is no support for speculations that in mammalian cells close proximity of homologoues sites is instrumental in functional cooperation.

Abstract: During meiosis I in males of the mole cricket Neocurtilla (Gryllotalpa) hexadactyla, the univalent X1 chromosome and the heteromorphic X2Y chromosome pair segregate nonrandomly; the X1 and X2 chromosomes move to the same pole in anaphase. By means of ultrastructural analysis of serial sections of cells in several stages of meiosis I, metaphase of meiosis II, and mitosis, we found that the kinetochore region of two of the three nonrandomly segregating chromosomes differ from autosomal kinetochores only during meiosis I. The distinction is most pronounced at metaphase I when massive aggregates of electron-dense substance mark the kinetochores of X1 and Y chromosomes. The lateral position of the kinetochores of X1 and Y chromosomes and the association of these chromosomes with microtubules running toward both poles are also characteristic of meiosis I and further distinguish X1 and Y from the autosomes. Nonrandomly segregating chromosomes are typically positioned within the spindle so that the kinetochoric sides of the X2Y pair and the X1 chromosome are both turned toward the same interpolar spindle axis. This spatial relationship may be a result of a linkage of X1 and Y chromosomes lying in opposite half spindles via a small bundle of microtubules that runs between their unusual kinetochores. Thus, nonrandom segregation in Neocurtilla hexadactyla involves a unique modification at the kinetochores of particular chromosomes, which presumably affects the manner in which these chromosomes are integrated within the spindle.

Abstract: Evidence is presented to support the proposition that the position of chromosomes within nuclei is determined by the following factors: (1) the location of centromeres on one side of the nucleus and telomeres(ends) on the other (reflecting the telophase orientation brought about by their poleward anaphase migration); (2) attachment of telomeres to the nuclear membrane (site of attachment in relation to the poles and equator being dependent on the length of the individual arms and point 1 above); (3) telomere-to-telomere attachment of nonhomologues in a specific sequence; (4) telomere-to-telomere attachment of certain homologous chromosomes.

Abstract: Male meiosis in autotetraploid Allium tuberosum (4×=32) is fairly regular, keeping in view its cytological status, with 81 percent of the chromosomes associated in quadrivalents and trivalents. About 5% of the cells have 32 univalents. Anaphase segregation is slightly irregular. While 48% of the pollen mitoses show 16 chromosomes, 87% of the mature pollen is viable as indicated by carmine or iodine staining. — Megaspore mother cells have 64 chromosomes associated in 32 bivalents at metaphase I. Anaphase segregation is normal. In three out of 56 cells studied multivalents, bivalents and univalents are observed as in male meiosis. — It is concluded that the species reproduces by pseudogamous parthenogenesis made possible by meiotic modification. This modification is almost perfect and almost completely specific for female meiosis. Slight effects are observed in male meiosis.

Abstract: Meiosis I of spermatogenesis in the fungus fly, Sciara coprophila, has a monopolar spindle which collects the maternal and supernumerary L chromosome sets, while the paternal chromosomes migrate away from the single pole to be excluded in a bud. By inspection, the metacentric paternal chromosome IV moves with its centromere lagging rather than leading the direction of motion. Therefore, we wondered if all paternal homologues move in such a reverse orientation. To determine the orientation of the other homologues which are acrocentrics (chromosomes II, III, X), their centromeres were localized by use of the DAPI C-banding technique. In addition, we characterized centromeric heterochromatin on polytene chromosomes by C-banding and in situ hybridization of satellite DNA isolated by Ag+-Cs2SO4 (ρCsC1 satellite I=1.698 g/ml; ρCsC1 satellite II=1.705 g/ ml). The two satellite fractions were localized to the centromeric heterochromatin of all the chromosomes, and to a varying degree to all chromosome telomeres. By DAPI C-banding we could precisely locate each centromere band on polytene chromosomes, and these results agreed with those of satellite cRNA in situ hybridization. We then applied the DAPI C-banding technique to primary spermatocyte preparations, and determined that all paternal chromosomes migrate at anaphase I with their centromeres lagging rather than leading movement to the cell periphery. Since in polytene chromosomes the X chromosome contains a moderately fluorescent band on its noncentromeric end as well, in order to clarify its DAPI C-banding result in primary spermatocytes, we did in situ hybridization of 3H nick-translated cloned rDNA, since rDNA is a convenient marker for the centromeric heterochromatin of the X. These data and the DAPI C-banding results indicate that the X as well as all the other paternal homologues display a reverse orientation (centromeres lag) as they migrate away from the single spindle pole to the cell periphery. — One model explaining this unusual paternal chromosome orientation is that there may be unique neocentromeric-like attachments to the non-centromeric free ends of these chromosomes. These attachments could serve to pull the paternal chromosomes to the cellular periphery as anaphase I progresses. In order to test this model, we analyzed anaphase I spermatocytes after a terminal block of heterochromatin had been removed from metacentric paternal chromosome IV by X-irradiation. We observed that when metacentric paternal chromosome IV is broken, it maintains its inverted “V” orientation rather than assuming a rod-like configuration. These data imply that there are no unique, terminal neocentromeric attachments to paternal chromosome IV as it progresses to the cellular periphery.

Abstract: Cells of a V79 subline of the Chinese hamster were microirradiated at wavelength 365 nm in the presence of the psoralen derivative, trioxsalen. Microirradiation was accomplished by a pulsed argon laser microbeam either in anaphase or in interphase 3 hr after mitosis. Inhibition of clonal growth and formation of micronuclei at the first postirradiation mitosis were observed after microirradiation of anaphase chromosomes and of small parts of the interphase nucleus. Microirradiation of the cytoplasm beside the interphase nucleus or between the sets of chromosomes moving apart from each other in anaphase did not produce these effects. Anaphase experiments showed that only the daughter cell which received microirradiated chromatin exhibited an abnormal growth pattern. Most interestingly, shattering of the whole chromosome complement could be induced by microirradiation of small parts of the interphase nucleus and post-treatment with caffeine. Since microirradiation of chromatin in the absence of psoralen was not effective, we consider formation of psoralen photoadducts to nucleic acids in microirradiated chromatin to be the specific cause of the effects. We suggest that DNA photolesions in chromosome segments present in the microirradiated part of the nucleus can induce shattering of all the chromosomes in the microirradiated nucleus. Several possibilities are discussed to explain this unexpected finding.

Abstract: Cells of a V79 subline of the Chinese hamster were microirradiated at wavelength 365 nm in the presence of the psoralen derivative, trioxsalen. Microirradiation was accomplished by a pulsed argon laser microbeam either in anaphase or in interphase 3 hr after mitosis. Inhibition of clonal growth and formation of micronuclei at the first postirradiation mitosis were observed after microirradiation of anaphase chromosomes and of small parts of the interphase nucleus. Microirradiation of the cytoplasm beside the interphase nucleus or between the sets of chromosomes moving apart from each other in anaphase did not produce these effects. Anaphase experiments showed that only the daughter cell which received microirradiated chromatin exhibited an abnormal growth pattern. Most interestingly, shattering of the whole chromosome complement could be induced by microirradiation of small parts of the interphase nucleus and post-treatment with caffeine. Since microirradiation of chromatin in the absence of psoralen was not effective, we consider formation of psoralen photoadducts to nucleic acids in microirradiated chromatin to be the specific cause of the effects. We suggest that DNA photolesions in chromosome segments present in the microirradiated part of the nucleus can induce shattering of all the chromosomes in the microirradiated nucleus. Several possibilities are discussed to explain this unexpected finding.

Abstract: The sequence of centromere separation in late metaphase/anaphase cells from a long term culture of cells from a male rat-kangaroo, Potorus tridactylus, was studied. The karyotype of

Abstract: Movement of chromosomes during mitosis appears to be coupled to the unidirectional turnover of spindle microtubules. This paper outlines a directional turnover model of mitosis which hypothesizes that: (1) Unidirectional turnover of tubulin subunits and microtubule-associated proteins occurs from an assembly site at one end to a disassembly site at the other end of mitotic apparatus microtubules. (2) The components of interpolar microtubules are continuously moving toward each pole due to their assembly in the opposite half spindle and disassembly in the near half spindle. (3) Mitotic chromosome movements are coupled to this directional turnover by selective formation of semi-stable lateral interactions or bridges between kinetochore microtubules and parallel interpolar microtubules. (4) The anaphase velocity of kinetochores relative to the poles is determined by the rate that kinetochore microtubules disassemble on their poleward ends minus the rate they assemble at their kinetochore ends. (5) Spindle elongation occurs when assembly of interpolar microtubules is more rapid than their disassembly or when interpolar microtubules slide in an anti-parallel arrangement. (6) The velocity of chromosome separation is the sum of spindle elongation and the poleward movements of sister chromosomes. Evidence for and against these hypotheses and some possible steps in the evolution of this type of mechanism are discussed.

Abstract: The three-dimensional structure of the spindle pole body (SPB) and meiotic spindle during early metaphase I through telophase I inPuccinia malvacearum is analyzed ultrastructurally from serial sections. During early metaphase I the spindle rotates from the perpendicular to a position oblique to the longitudinal axis and parallel to the sagittal plane of the cell. Tubular cisternae are present within the spindle at this stage. The half middle piece (MP) subtends a collateral disc (co-disc) which is inserted eccentrically within each SPB. The SPB, co-disc and half MP at opposite poles are in mirror image. During the transition from early metaphase I to full metaphase I, the spindle orients parallel to the lateral wall of the promycelium and the half MPs are lost. The co-discs partially detach from each discoid SPB and maintain this relation until the end of interphase I. Co-discs become further differentiated as they attach to the subtending sheath-like extension of the nuclear envelope previously occupied by the half MPs. Microvesicles within the nucleoplasm are specific to mid metaphase I. A metaphase plate is absent. The 14 bivalents, which are directly connected to each polar SPB by 2 to 3 kinetochore MTs, are spread over nearly the entire length of the central spindle. The first anaphasic movement involves asynchronous shortening of the kinetochore MTs while the second consists of extensive pole-to-pole elongation. Astral MTs first appear at early metaphase I and become most numerous at anaphase I. An intact nuclear envelope constricts against the central spindle at either end of the interzonal region. Concurrently, centripetal growth of the nuclear envelope under each SPB results in their gradual externalization by the end of telophase I. The sibling nuclei are cut off by constriction of the nuclear envelope at either end of the interzonal region. These meiotic stages inP. malvacearum are compared with those in other basidiomycetes and ascomycetes.

Abstract: In meiosis-I crane-fly spermatocytes 3 autosomal half-bivalents move to each pole in anaphase while the 2 sex-chromosomal univalents remain at the equator. The sex chromosomes move to opposite poles only after the autosomes reach the poles; the sex chromosomes start to move polewards about 25 min after the autosomal half-bivalents have begun to move. We irradiated portions of single autosomal spindle fibres with an ultraviolet microbeam and found that these irradiation altered the subsequent sex-chromosome movements. Two effects were observed. In one, one of the sex chromosomes did not move at all; the sex cin after the autosomal half-bivalents have begun to move. We irradiated portions of single autosomal spindle fibres with an ultraviolet microbeam and found that these irradiation altered the subsequent sex-chromosome movements. Two effects were observed. In one, one of the sex chromosomes did not move at all; the sex cin after the autosomal half-bivalents have begun to move. We irradiated portions of single autosomal spindle fibres with an ultraviolet microbeam and found that these irradiation altered the subsequent sex-chromosome movements. Two effects were observed. In one, one of the sex chromosomes did not move at all; the sex chromosome that remained at the equator would normally have moved to the pole associated with the irradiated autosomal spindle fibre. In the second, both sex chromosomes moved to the same pole, always that of the non-irradiated side. These effects occurred whether or not autosomal anaphase movement was blocked by the irradiation. There was no wavelength dependence for altering sex-chromosome movements. Sex-chromosome movements were altered only when at least one sex-chromosomal spindle fibre was adjacent to the irradiated autosomal spindle fibre; when neither sex chromosome had a spindle fibre adjacent to the irradiated autosomal spindle fibres the chromosomes always moved normally. Irradiation of sex-chromosomal spindle fibres during sex-chromosomal anaphase showed short blockages of movement (usually 5-8 min), and then complete recovery. Direct irradiation of sex-chromosomal spindle fibres (without irradiating autosomal spindle fibres) when the autosomes were in anaphase but the sex chromosomes were in metaphase never caused abnormal sex-chromosome movements. These results eliminate the possibility that when we irradiated autosomal spindle fibres that were adjacent to sex-chromosomal spindle fibres the sex-chromosomal spindle fibres were irradiated inadvertently and were unable to recover from the damage. We suggest that the irradiations of autosomal spindle fibres alter a control system involved in "turning on' sex-chromosomal spindle fibre motors, rather than directly altering the motors. We suggest that interactions between spindle fibres are somehow involved in this control system.

Abstract: The mitotic nuclear (equivalent to cell) cycle of the oomycete fungus, Saprolegnia ferax, was analysed by quantitative serial-section electron microscopy of hyphal nuclear populations synchronized by inhibition of DNA synthesis by fluorodeoxyuridine (FdUrd). Following telophase and karyokinesis, kinetochore mitrotubules persist into G1 stage as a single group of approximately 42 per nucleus (2n = 42 for this species). During G1 the centrioles replicate and kinetochore microtubules separate into 2 groups of approximately 21, a configuration they retain through S and G2. During metaphase a new population of kinetochore microtubules are formed, each one of an amphitelic pair connecting to the opposite pole to that associated with the persistent microtubule from the previous division. Thus, by the end of metaphase, there are approximately 42 kinetochore microtubules per half spindle. FdUrd, applied for 2 h with uracil, completely blocks DNA synthesis yet permits centriole replication and causes nuclei to accumulate with 2 pairs of centrioles, 2 arrays (each of 21) of kinetochore microtubules, and apparently enlarged nucleoli. Removal of FdUrd permits rapid (within 30 min) DNA synthesis followed by successive rounds of decreasingly synchronous nuclear cycles. These post-FdUrd cycles are 2.5 times longer than normal at 2.5 h, with S plus G2 being more extended than other phases. Calculated durations of a normal nuclear cycle are: G1, 33 min; S, 7 min; G2, 10 min; metaphase, 8 min; anaphase, 0.5 min; and telophase, 4 min.

Abstract: The ultrastructural features of chromosome vesicle formation in early sea urchin embryos and chromosome vesicle uptake of tritiated thymidine is described. Envelopes which resemble typical nuclear envelopes form around the condensed anaphase chromosomes. In late anaphase or early telophase, the chromosomes swell and decondense and it is at this time when tritiated thymidine is incorporated. This study shows that DNA synthesis in the rapidly dividing cells of early sea urchin embryos occurs in chromosome vesicles which form during anaphase.

Abstract: Cell division is described in the octaflagellate prasinophyte Pyramimonas amylifera Conrad and is compared in related genera. Basal bodies replicate at preprophase and move toward the poles. Cells remain motile throughout division. The nuclear envelope disperses and chromosomes begin to condense at prophase. Pairs of multilayered kinetochores are evident on the chromosomes of the metaphase plate. Spindle microtubules extending from the region of the basal bodies and rhizoplasts attach to the kinetochores or extend from pole to pole. Numerous vesicles and ribosomes have entered the nuclear region and the incipient cleavage furrow invaginates. The chromosomes move toward the poles at anaphase leaving a broad interzonal spindle between the two chromosomal plates. The nuclear envelope reforms first around the chromatin on the side adjacent to the spindle poles and later on the interzonal side. The cleavage furrow progresses into the interzonal spindle at telophase. By late telophase the nucleoli have reformed and the chromosomes have decondensed. The interzonal spindle has not been observed late in telophase. As the cleavage furrow nears completion the cells begin to twist and contort, ultimately separating the two cells.

Abstract: It has long been recognized that anaphase consists of two distinct motile events: movement of chromosomes to the poles, and the separation of the poles (spindle elongation). In the mammalian spindle, e.g. PtK1 cells, the chromosomes move at one speed until they reach a separation about equal in length to the original metaphase spindle, then they slow down (Brinkley and Cartwright 1971; Cande 1978). Chromosomes and poles then move together until the spindle is about twice its original length. Structural studies of the arrangement and redistribution of microtubules at anaphase suggest that each motile event may be associated with a particular class of microtubules (Fuge 1977; McIntosh et al. 1975; McDonald et al. 1977; Inoue and Ritter 1978). The chromosome movement to the poles is associated with kinetochore microtubules and spindle elongation with nonkinetochore microtubules, especially the central spindle. These stages of anaphase may also represent two separate physiological events. Chloral hydrate blocks spindle elongation but not chromosome-topole movement in insect spermatocytes (Ris 1949). Likewise, dilute colchicine blocks spindle elongation but not the initial fast chromosome movements (Oppenheim et al. 1973). Thus, it has been suggested that more than one mechanochemical system may be functioning during mitosis.

Abstract: Cytological observations were made on spike primordia as well as root and leaf meristems of hybrids between Hordeum vulgare and H, bulbosum (2x) to elucidate mechanism of chromosome elimination. High frequencies of cells with micronuclei were observed in spike primordia of the hybrids examined. The average percentages of cells with micronuclei in three different hybrids were 16.8% (R25788), 12.9% (S92-201) and 7.9% (S130-200). About 40% of spike primordium cells of R25788 had fewer chromosomes than the 14 expected in a diploid hybrid. On the other hand, in root and leaf meristems of R25788, percentages of cells with micronuclei were 2.3% and 2.4%, respectively. Also, 94.6% of root meristem cells of R25788 had the expected hybrid chromosome number. Thus, chromosome elimination in hybrids between H. vulgare and H. bulbosum appears to be a tissue-dependent phenomenon, perhaps related to the extent of differentiation required.Disturbances in nuclear division were also examined. Percentages of cells with non-congressed chromosomes at metaphase and lagging chromosomes at anaphase were 15.2% and 20.7%, respectively in spike primordia of R25788. These percentages are similar to those of cells with micronuclei in spike primordia of R25788. It is suggested that failure of congression of some chromosomes during prometaphase is the main mitotic disturbance leading to chromosome elimination.

Abstract: The relationship between progression through anaphase and furrow establishment was investigated in PtK1 cells using the anti-mitotic agent Nocodazole to arrest cells at different points in anaphase The capacity of cells to furrow was compared to the kinetochore-kinetochore separation attained at the time of arrest For the stages of anaphase examined, furrowing capacity increased directly with kinetochore-kinetochore separation until complete furrows were formed after kinetochore-kinetochore separations of 14 μm or more were reached Furrow establishment thus occurs during a definite interval during anaphase in PtK1 cells Results from electron microscopy of both Nocodazole-treated and control cells suggest that a population of astral microtubules may be important for furrow establishment

Abstract: Cell division of a haptophyte,Cricosphaera roscoffensis var.haptonemofera Inouye et Chihara, was examined by electron microscopy. Onset of cell division is characterized by many kinds of cell organelle behaviour; migration of the nucleus toward the cell anterior, replication of basal bodies and haptonema, chloroplast division and proliferation of rough-ER. Flagellar roots of a complex structure do not duplicate during cell division. At prophase the nuclear envelope is vesiculized and the cytoplasmic microtubules, which probably are transformed from the flagellar roots, invade the nucleoplasm through gaps in the nuclear envelope. Condensed chromosomes in prophase form a typical equatorial plate, but later individuality of chromosomes becomes obscure. The spindle microtubules converge on opposite poles. Basal bodies or centrioles lie at the lateral sides of the poles. Microtubules converge in the rough-ER-mitochondria complex occupying the polar area. The equatorial plate is conspicuously surrounded by the membraneous precursor of the daughter nuclear envelope. In anaphase the equatorial plate divides into 2 plates and each moves toward the opposite poles. During the separation of the daughter chromatin plates toward the ends of the cell, the interzonal spindle microtubules proliferate conspicuously and extend between the two daughter plates. These events are accompanied by the development of the nuclear envelope, formed from the fusion of vesicles present around the equatorial plate. The immature daughter nuclear envelope invaginates to enclose the chromatin, pinching off a bundle of the interzonal microtubules. The interzonal spindle is cut at the equatorial level by the ingrowing of peripheral-ER, leading to cytokinesis. Cytokinesis is accomplished by furrowing of plasmalemma. After cytokinesis and nuclear division, the interzonal spindle halves remain persistent, not detached from the daughter nuclei. They will become the flagellar roots in the vegetative cell.

Abstract: A plant having spontaneous multiple translocations was isolated in the normal populations of Chilli cultivar CA-960. The plant was very healthy having broad green leaves and big size flowers. The chromosome behaviour was studied from the anther smears. At metaphase I rings of 4 and 8 chromosomes and chains of 4, 6, 8, 10, 12, and 18 chromosomes were observed in most of the microsporocytes studied. Regular formation of bivalents and univalents were also noted. Nondisjunction and irregular distribution of chromosomes, laggards and chromatin bridges were observed at anaphase I.All these irregularities lead to the formation of unbalanced spores resulting in 90 to 100% sterility. The probable reasons for these anomalies are discussed.

Abstract: 1. Observations of the chromosomal arrangement and behavior were made in the meristematic cells of the root tips of H. gracilis (2n=4) and C. capillaris (2n=6).2. In the prophase and telophase nuclei, the centromeric regions of chromosomes were localized in a relatively small area of the nuclear envelope. During prometaphase, the centromeric regions migrated toward the equatorial plane, keeping their arrangement at prophase. During anaphase, the relative arrangement of the chromosomes was the same between the two separating chromosomal groups. These observations suggested that the relative arrangement of chromosomes is likely to be retained through the mitotic cycle.3. In the two nuclei of two adjacent cells, or of the binucleate cells induced by caffeine, the occurrence of the same relative chromosomal arrangement pattern was significantly high. This fact also seems to support the suggestion mentioned above.4. In H. gracilis, non-random manner of chromosome disposition was revealed from a statistical approach. While in Crepis, a pair of nucleolar chromosomes deviated from random disposition and showed some tendency of lying side by side. Derivation of this non-random disposition was discussed briefly, and it was conjectured from all observations that the individual chromosomes are essentially independent in occupying their spatial positions.