| In this experiment, we studied the germination of pollen grain and the growth of pollen tube by fluorescence microscope, seed setting rate by removing stigma, and by light microscope and electron microscope observed the changes of polar nucleus in two days of rice, wheat and barley. The main results were as follows:(1) Rice pollen grain started to germinate two minutes after it reached the stigma. Half an hour later, the pollen tube reached the embryo sac, and it grew in stigma less slowly than grew in style and ovary. The pollen grain of wheat and barley started to germinate in three minutes, and the growing process of pollen tube was similar to rice's.(2) After the pollen tube arrived at the base of the embryo sac, it would enter into it from a degenerated synergid and release two sperm cells. It was found that the synergid had degenerated before pollination in rice and wheat, while barley's synergid degenerated after the embryo sac mutured but before pollen tube's arrival.(3) After the sperm cells entered into embryo sac, they would move near the top of degenerated synergid where was of thin cell walls. So the two germ cells would enter into the egg cell and the central cell easily. Although the sperm nucleus came to the egg nucleus earlier, its nucleus fusion finished less slowly than that of the sperm nucleus and the polar nucleus. It was found that rice's polar nucleus fertilized in 2～4 hours after pollination, while the polar nucleus fertilization finished in 3～5 hours.(4) After fertilization, zygote would undergo a period of dormancy, while the primary endosperm nucleus began to divide into free endosperm nuclei soon.(5) The free endosperm nucleus of rice, wheat and barley all was larger than other cell's nucleus, and its nucleolus could be deeply stained. The free endosperm nucleus had heavy cytoplasm containing abundant organelles in active condition. The free endosperm nucleus of rice was nearly round, while wheat and barley's was basically oval.
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