stages of pollination and fertilization of pine. sexual process of pine from formation of female gametophyte, to fertilization

anatomy archegonia archegonium background biology botanical botany conifers development egg embryo endosperm female fertilisation fertilization gametophyte grain gymnosperms illustration integument isolated male megagametophyte megasporangium megaspore megasporocytes microgametophyte micropyle microscopic morphology ovule phytomorphology pine pinus plant pollen pollination process schema scheme scientific sexual sperm sporangia spruce stage structure tube white