The ovule contains the inner and outer integument. The endosperm is also called the albumen of the seed. The pollen tube releases two sperm nuclei into the ovule. The evolutionary origin of the inner integument which is integral to the formation of ovules from megasporangia has been proposed to be by enclosure of a megasporangium by sterile branches telomes. Retrieved from " https: The cell closest to the micropyle opening of the integuments differentiates into the egg cell, with two synergid cells by its side that are involved in the production of signals that guide the pollen tube. Back Issue Covers Gallery. In gymnosperms, three of the four haploid spores produced in meiosis typically degenerate, leaving one surviving megaspore inside the nucellus.
