When a pollen grain germinates, a pollen tube pushes its way out through an aperture in the pollen grain wall,and the nuclei migrate into the tube.是什么意思_When a pollen grain germinates, a pollen tube pushes its way out through an aperture in the pollen grain wall,and the nuclei migrate into the tube.在線(xiàn)翻譯_英語(yǔ)_讀音_用法_例句