| Popis: |
Periodic collections of 1-yr-old pistillate cones were made from four Pinus rigida trees in the Ecology Forest and from several trees in the Control Forest at Brookhaven National Laboratory between 26 June and 15 July 1963. The experimental trees were growing in a natural pine-oak forest that was irradiated by a 137 Cs (9500 Ci) source. Beginning on 22 November 1961, the forest was exposed to γ-rays during 20 hr each day. In excess of 1000 ovules were dissected from cones exposed to radiation levels of 1·15, 2·15, 2·80 and 3·15 R/20-hr day. Serial microtome sections were used to determine the effect of radiation on fertilization. Fertilization was delayed by chronic γ-exposure, and this delay amounted to about 7 days when the controls were compared to the trees at the highest exposure level 3·15 R/20-hr day. In addition, chromosomal aberrations were also observed in several cells during mitosis. Chromosomal bridging was observed at anaphase in cells from nucellar tissue of a cone exposed to 2·80 R/20-hr day and micronuclei were present in an ovule which had received 3·15 R/20-hr day. Photomicrographs were made to illustrate embryo sac development at various stages and the chromosomal aberrations occurring at two levels of radiation. |
