The organ in which megaspores are formed. The megaspore gives rise to a female gametophyte in ferns and in seed plants, and in flowering plants becomes the embryo sac. A region of a plant in which active cell division occurs, the cells of the meristem being undifferentiated into a specialized form. Meristematic tissues occur at the root and shoot tips giving growth in length. A small canal in the integument surrounding the ovule of a flowering plant, through which the pollen tube usually enters the ovule on the way to the embryo sac.
Water enters the seed via the micropyle prior to germination.
In Tracheophytes the microspore is the pollen grain. A spiral series of overlapping scales making up the female or ovulate cone with each scale producing two ovules on the upper surface. Often brightly colored, the petal is a modified leaf and is important in flowers pollinated by insects. The two nuclei that are formed at each pole of the angiosperm embryo sac. They will fuse with a male nucleus to form a primary endosperm nucleus.