Fundamental Studies on Mating in Forest Trees (I)
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概要
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This experiment was undertaken for the purpose of determining the most favorable time of pollen collection. 1) Pollen mother cells started meiosis in early March, and pollen tetrads were formed between the second half of mid March and the first half of late March. The first metaphase of meiotic division was observed mostly during the period of March 16_??_21. The period of meiosis was about 20 days. Irregular meiotic division was hardly observed, with the exception of the chromosome bridges. Meiosis seemed to be done when the mean temper-ature rose to 6_??_10°C. 2) Immature pollen grains after the separation from tetrads grew rapidly in the second half of late March, and in early April they attained much the same size as the mature pollen grains. In early April (5_??_7 days before pollen discharge), the immature pollen grains did mitotic division and developed into the mature pollen containing a reproductive cell and a pollen tube cell. The mature pollen began to discharge from about April 10. The number of days required from tetrad formation to pollen discharge was about 25days. 3) From the artificial germination test, the first pollen germination was observed in the pollen sowed on March 26 (about 15 days before pollen discharge). Thereafter, the germi-nation of pollen rose gradually with pollen development, and by April 6 (about 4 days before pollen discharge) attained almost the same percentage as mature pollens. All germinated pollen grains had two kinds of generative and pollen tube nuclei. Therefore, it is thought that immature pollen grains having a nucleus do mitotic division after being sown on agar medium and after that they germinate. 4) From the results of the morphological investigation and germination test, we may conclude that the most favorable time for pollen collection is the time of pollen shedding, but even several days before that the collection of pollen is practicable.
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