• D. Lewis

      Articles written in Journal of Genetics

    • Genetical studies in apples. II

      D. Lewis M. B. Crane

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      The inheritance of a “purple anthocyanin” character in apples is described.Malus Neidzwetzkyana was found to differ fromM. Malus in having a single dominant gene for “purple pigmentation”. Great variation was found within the “purple” plants, probably due to the segregation of modifiers.

      A technique for increasing the percentage of germination by removing the testa is described. The percentage of scorable plants was increased from 56 to 99. No differential viability of the “green” and “purple” embryos was found.

    • Genetical studies in cultivated raspberries - I. Inheritance and linkage

      D. Lewis

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    • Genetical studies in pears - III. Incompatibility and sterility

      M. B. Crane D. Lewis

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    • Genetical studies in pears - IV. Pollen-tube growth and incompatibility

      D. Lewis I. Modlibowska

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      1. Self-incompatibility in diploid pears is due to arrested pollen-tube growth. Three days after pollination the tubes are approximately one-third of the way down the style and their ends are swollen.

      2. In a cross between two diploid varieties compatible and incompatible tubes are present indicating gametic determination of incompatibility.

      3. The somatically doubled autotetraploid Fertility is self-fertile, but both compatible and incompatible tubes are present in selfed styles. Compatible tubes of the tetraploid grow faster than compatible tubes of diploids both in tetraploid and in diploid styles.

      4. The breakdown of the self-sterility mechanism following chromosome doubling is reviewed and found to be of fairly widespread occurrence in plants. A working hypothesis to explain the effect of polyploidy on self-sterility is given: it is based on the assumption thatS1S2 pollen is compatible andS1S1 andS2S2 pollen incompatible inS1S1S2S2 styles.

      5. Pollen tubes of the diploid variety Beurré Bedford grow as fast as those of a tetraploid variety, penetrate the style and enter the embryosac; but only rarely do they effect fertilization. Beurré Bedford pollen grains are unreduced pollen mother cells with haploid, diploid, triploid, and tetraploid nuclei. The high rate of growth of the pollen tubes is due to the nature of the pollen cell and the failure to fertilize the eggs to the lack of balance between the sperm nuclens and the cell.

      6. The result of this normal pollen-tube growth without fertilization is the formation of seedless fruits.

    • Physiology of incompatibility in plants - III. Autopolyploids

      D. Lewis

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    • The incompatibility sieve for producing polyploids

      D. Lewis

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      Heat-shocks applied to the pollen mother cells, followed by self-pollination is effective in producing triploids in fruit trees. The method depends upon the sieve-like action of incompatibility on the pollen, allowing only diploid pollen tubes to reach the ovary, although much of the pollen is haploid. Since only pollen grains which carry two differentS genes are compatible the heat-shock must be given before these genes segregate.

      By this method triploids have been produced from diploid pears. In diploid cherries, fruits have been obtained, but the seeds were small and inviable. In a self-incompatible plum (2n = 32), fruits and seeds were formed after self-pollination with treated pollen, but the seedlings had the same chromosome number as the parent.

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