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Ever since the first report of cytomixis in Oenothera gigas and O. biennis by Gates (1911), this cytological abnormality, characterized by the migration of chromatin/chromosomes from one cell into the cytoplasm of adjacent cell, has been observed in a good number of species by several workers

The 2C and 4C nuclear DNA amounts were estimated in eight diploid species, belonging to three diverse genera (Vicia, Tephrosia, and Phlox) and their corresponding colchitetraploids. In P. drummondii, T. purpurea, and T. oxygona tetraploids the deviation from the expectation was highly significant. The DNA in P. drummondii was further discarded in subsequent (C1, C2) generations, thus attaining an overall reduction of about 25%. The DNA content in the subsequent generations was the same as that of C2. It is concluded that rapid DNA loss in the first and subsequent generations was not only associated with the substantial increase (30-66%) in the seed set, but it also helped in the establishment and stabilization of the tetraploid. The possible relationship between such a nucleotypic change and success of polyploids is discussed. The DNA change from the expected value in the P. drummondii tetraploid was achieved by equal decrement to each chromosome independent of size, i.e., small chromosomes loose the same amount of DNA as the large chromosomes.

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Comparative studies on male and female meiosis in diploid (2n = 2x = 14) and colchitetraploid (2N = 4x = 28) ornamental Phlox drummondii reveal higher chiasma frequency in embryo‐sac mother cells as compared with pollen mother cells in the diploid, and significant differences in the pairing properties of chromosomes in the pollen mother cells and embryo‐sac mother cells of the colchitetraploid. Male meiosis in the colchicine‐induced autotetraploid was abnormal with 51.70% of chromosomes associated in quadrivalents and tridents in 96% of the cells. This was followed by discordant anaphase I disjunction. In the female meiocytes the chromosomes formed 14 bivalents in 86.66% of the cells. Quadrivalents (1–3) appeared only in 13.34% of the cells. It is concluded that meiosis in male and female cells of the colchitetraploid is governed and regulated by different controlling systems of gene(s).

Meiotic studies carried out on seven plants/clones of Tradescantia spathacea did not show the expected ring of 12 chromosomes in any of the 1765 cells studied at diakinesis (1202 cells) and metaphase I (563 cells). While at diakinesis the chromosomes resolved into chain configurations of all lengths ranging from one through 12 chromosomes, with the mean per cell being 2.47 ± 1.28, at metaphase I chains carrying up to 10 chromosomes were seen and the mean per cell was 4.18 ± 1.47. However, the larger chains were not the most frequent configurations observed at the two stages. Bivalents and univalents were the most frequent configurations observed in 38.68 and 43.92% cells at diakinesis and 63.94 and 57.72% cells at metaphase I, followed by chains of 10 (29.95% cells) and chains of three (51.50% cells) at the two stages, respectively. The larger chains, though visible at both the meiotic stages, varied significantly in the centromere orientation patterns. While at diakinesis they predominantly showed linear or indifferent orientation, at metaphase I 83.25% chains showed alternate orientation, with the rest showing linear and/or indifferent orientation. A high frequency of alternate orientation was observed in chains of three chromosomes (93.93%), followed by the chains of five and four, where 74.19 and 71.27% chains appeared in alternate orientation, respectively. In 4.97% cells with two chains of six chromosomes each, contrasting behavior was noticed in the two chains in respect of orientation. While one chain appeared zigzagged with alternate centromeres facing the same pole, the other chain invariably appeared in linear configuration. As a result of complex configurations at metaphase I and the high frequency of univalents, anaphase I segregation of chromosomes was highly irregular with 84% cells showing 1-3 lagging chromosomes. The average pollen viability determined for the seven clones studied was very low (17.87 ± 2.57%). The probable cause(s) of the different behaviors of the chain multiples at the two meiotic stages is discussed.

Comparisons of the chromosome numbers, 2C nuclear DNA amounts and karyomorphology were made in explant cultures of diploid (2n = 2x = 14) and autotetraploid (2n = 4x = 28) Phlox drummondii. In 6-36 week old calli derived from diploid internodal segment explants, and in cells of root tips regenerated from such callus, marked differences were observed in chromosome number. The chromosome numbers ranged from 2n = 14 to 2n = 100 and DNA amounts from 8.20 to 63.20 pg in the diploid derived callus, while the extent of variation was much reduced in the regenerated roots. In contrast, the autotetraploid cultures were characterised by the maintenance of the same chromosome number and DNA amounts as the mother plant. Modified chromosome structures were not apparent in any of the cultures. The possible reasons for the chromosomal instability at the diploid level and stability at the tetraploid level are discussed.