Parallel lines of first and selfed back-cross populations of longiflora-glauca-longiflora hybrids involving both the standard and variant species of N. glauca (N. glauca W. 8400) were raised and studied. The variant W. 8400 maintained its heterozygosity even in the selfed back-cross progenies. Variations in plant habit, leaf characters and flower types were observed in high frequency as a consequence of chromosomal segregation. The chromosome number ranged in the progenies from 20 to 40. By the complete pairing of the two races of glauca it is evident that they are identical cytologically. Pairing was complete in the back-cross between the 20 longiflora chromosomes with additional varying number of glauca univalents. The presence of glauca univalents suppressed the longiflora characters whereas the presence of longiflora univalents in addition to the diploid level of glauca complements, did not alter the basic glauca characters. The possibilities and utility of building up of races with addition of alien chromosomes in the longiflora-glauca combination are discussed.
1. The chromosome number and karyotype of Smilacina racemosa vars. racemosa and amplexicaulis, S. stellata vars. stellata and sessilifolia, and S. paniculata are reported. 2. S. racemosa var. racemosa in eastern North America contains tetraploid (2n=36), octoploid (2n=72), and 16-ploid (2n=ca. 144) chromosomal races, with the octoploid the most common. No obvious gross morphological variations seem to be correlated with the different polyploid types. 3. Previous reports for the tetraploid (2n=36) nature of the western North American S. racemosa var. amplexicaulis and S. stellata var. sessilisfolia, as well as the eastern var. stellata, were verified. 4. Costa Rican material of the widespread Central American S. paniculata proved to be likewise tetraploid (2n=36). The same basic karyotype formula (K(n)=3V+7J+8v) was found for all the North and Central American taxa studied and coincides with that reported by other authors for several Asiatic species of Smilacina. 5. The distribution of Smilacina in the three widely separated main survival areas of the ancient Arcto-Tertiary Geoflora generally, and the close ecological relationships to temperate montane subtropical forests with prominent Arcto-Tertiary influence especially, suggests that this genus has had a common evolutionary history not only with this Geoflora, but in particular with such cloud forest habitats. Though the great similarity of some species suggests recent long-range dispersal, the great variety of species in Central America would point to a Tertiary, and not a Pleistocene origin of the disjunct Arcto-Tertiary elements there. Since the basic karyotype of all Smilacina species (with a slight exception in the highly specialized S. trifolia) is apparently remarkably uniform throughout the genus, its particular configurations must therefore date back to at least the middle Tertiary, when interchange between Old World and New World Arcto-Tertiary floristic areas was still possible. Thus, despite tremendous migrations, gross morphological changes and speciation, this basic Smilacina karyotype has remained unchanged for extremely long periods (perhaps 50 million years?).
The complete pachytene complement of 18 bivalents from a single pollen mother cell of Hibiscus cannabinus is described. The bivalents are differentiated into short chromatic proximal regions and long achromatic distal regions which terminate without telochromomeres. Morphological relationships do not suggest that the present basic chromosome number of 18 arose by polyploidy from 9-chromosome genomes. Distal segment ratios, however, fall more or less into six groups of three, which may reflect ancient origin from 6-chromosome genomes.
The present study deals with the effect of colchicine-gammexane treatment on Foeniculum vulgare which leads to the production of tetraploid, mixoploids and diploid plants which exhibited pollen variability. E. 139. In this 2n plant the cytological behaviour was normal but it had 90% variable pollen grains which included giant and bichambered grains also. E. 147. Though diploid it showed multivalent formation. Meiosis is considerably irregular. It also exhibited cytomixis and syncyte formation. Nuclear migration between cells takes place as late as T. II. E. 151. In this diploid plant a good proportion of PMC's had normal stages but a few showed laggards, strays and bridges. It exhibited development of exceptionally large giant pollen grains resembling embryosac like structures. It had giant as well as joined pollen grains which show transfer of nuclei and cytoplasmic material from one grain to another. E. 182. (4n) The meiotic instability was considerable. It is characterised by very low frequency of multivalents. The possibility of certain genes controlling the pairing has been discussed. This plant also exhibited splitting of nuclei at T. I which resulted into multiple spindles at M. II. This is caused by the splitting of the spindle organizers.
Incidence of polyploid cells were studied in leukocyte cultures established from radiation-exposed people, as well as from human blood irradiated in vitro with 60Co at the dose from 50 r to 350 r. Polyploid cells were extremely frequent in the radiation-exposed subjects than in the normal ones. A high frequency of polyploid cells was also obtained in leukocytes cultured from the blood irradiated in vitro. The frequency of polyploid cells increased with the dose of radiation. The majority of the polyploid cells contained abnormal chromosomes such as dicentrics, tricentrics, rings, some other related ones, and acentric fragments. Among them dicentrics were most frequent in occurrence. The frequency of polyploid cells showing chromosome abnormalities increased with the dose of radiation. Very often the abnormal chromosomes were present in pair, as a set of two morphologically identical chromosomes, in most cells lying in the tetraploid range; while they occurred in two pairs in cells in the octoploid range. Evidence presented is suggestive of that the polyploid cells might be originated from affected cells with abnormal chromosomes such as dicentrics as may interfere with cell division, the distribution of chromosomes to the daughter cells being omitted after chromosome replication.
Fourteen patients with sexual abnormalities have been investigated for their chromosomal conditions. Eleven of the 14 cases had an apparently normal karyotype, 2 patients exhibited sex-chromosome mosaicism of the XY/XO, and one was XX/XXY mosaic. One of the two XY/XO mosaics is probably fertile. The importance of chromosomal studies on more than one tissues and a detailed histological examination of the gonads in cases with sexual abnormalities in general and suspected mosaicism in particular, has been emphasized.
Further proof is provided for the view that the chromosomes in the macronucleus ofBlepharisma and Spirostomum are in the nature of organized Feulgen positive filaments disposed within its membrane. Under appropriate conditions, the filaments unwind themselves from the macronucleus to give rise to greatly elongate structures.
1. RNA accumulated during the course of regeneration in both the macronucleus and cytoplasm of stentors. Levels were higher at eight hours near the end of regeneration than at four hours. 2. With both actinomycin D and 5-flurouracil, levels which inhibit RNA synthesis in mammalian cells were initially ineffective in suppressing regeneration in stentors, but after exposure for relatively long periods, levels of macronuclear and cytoplasmic RNA was reduced, and regeneration was inhibited. 3. Very high levels (15-25 γ/ml) of actinomycin D will inhibit regeneration in stentors if added before achievement of stage four, but if added at the sixth hour, regeneration is completed. The critical product emanating from the macronucleus prior to stage four is probably messenger RNA. 4. The results obtained with both actinomycin D and 5-flurouracil suggest that the high degree of polyploidy of the macronucleus protects the organism from the effects of antimetabolites which operate on genetic loci. 5. RNase at 0.5 mg/ml concentration prevented regeneration, and appeared to physiologically destroy RNA in the stentors, but organisms which had almost been depleted of RNA were able to regenerate after a very short lag period.
1. By a technique of rotation-mediated cultivation, cells dissociated from brain 6- to 9-day chick embryos were cultured in vitro. Both cerebral and midbrain cells dissociated from successively older embryos made progressively smaller aggregates. It is suggested from the observation of histogenesis in the aggregates that the decrease in the size of aggregates may be related to the cellular differentiation. 2. In Eagle's basal medium containing bovine serum in various concentrations, a largest aggregates in size were formed with 10% or 20% serum. Aggregates cultured in Eagle's basal medium alone showed an approximately similar size to those cultured with 5% or 40% serum, but the former showed a sign of necrosis. These results indicate that serum seems to have no direct effect on the cell-to-cell contact, although it may be necessary for general cell metabolism. 3. Aggregates of the cerebrum, the midbrain, and the neural-retina cells from 7 1/2-day chick embryos were cultured for varying days. Aggregates of cerebral cells and midbrain cells showed a rise in size. This may be due to cell growth, or the formation of fibres. Aggregates of neural-retina cells showed changes in size produced by the fusion or fragmentation of the aggregates. 4. Commingled aggregates of cerebral and neural-retina cells showed a histogenesis in which the neural-retina tissue is arranged concentrically around the cerebral tissue. This may indicate that a sorting out took place between the cerebral cells and the neural-retina cells. As a result of these facts, the meanings of changes in aggregation patterns were discussed. This work was aided in part by Grant No. RF-00058 (to Y. Kuroda) from the National Institutes of Health, U. S. P. H. S.. The author wishes to express his deepest appreciation to Assistant Professor Y. Kuroda, for his constant interests and advices throughout the course of this investigation and the reading of this manuscript.
Chromosome numbers are reported for 15 species of Dioscorea and Rajania. All are multiples of the base number, 9. Three new cases are reported of both 36 and 54 chromosome plants in a single species. The possible modes of origin of hexaploids are discussed. Colchicine induced octoploids were used to synthesize 54 chromosome plants of D. floribunda. All such hexaploids were highly infertile. Guard cell lengths were correlated with level of ploidy and provided a rapid screening technique for finding higher polyploids.