development of embryo from the cells of the nucellus is called metamorphosis.
development of embryo from the cells of the nucellus is called metamorphosis.
development of embryo from the cells of the nucellus is called?
metamorphosis
after fertilization, the nucellus may develop into the "perisperm" that feeds the embryo. in some plants, the diploid tissue of the nucellus can give rise to the embryo within the seed through a mechanism of asexual reproduction called nucellar embryony.









































section::::ovule parts and development.:megagametophyte.









































the haploid megaspore inside the nucellus gives rise to the female gametophyte, called the "megagametophyte".









































in gymnosperms, the megagametophyte consists of around 2000 nuclei and forms archegonia, which produce egg cells for fertilization.
ovule
the pollen grains are dispersed by the wind to the female, ovulate cone that is made up of many overlapping scales (sporophylls, and thus megasporophylls), each protecting two ovules, each of which consists of a megasporangium (the nucellus) wrapped in two layers of tissue, the integument and the cupule, that were derived from highly modified branches of ancestral gymnosperms. when a pollen grain lands close enough to the tip of an ovule, it is drawn in through the micropyle ( a pore in the integuments covering the tip of the ovule) often by means of a drop of liquid known as a pollination drop. the pollen enters a pollen chamber close to the nucellus, and there it may wait for a year before it germinates and forms a pollen tube that grows through the wall of the megasporangium (=nucellus) where fertilisation takes place. during this time, the megaspore mother cell divides by meiosis to form four haploid cells, three of which degenerate. the surviving one develops as a megaspore and divides repeatedly to form an immature female gametophyte (egg sac). two or three archegonia containing an egg then develop inside the gametophyte. meanwhile, in the spring of the second year two sperm cells are produced by mitosis of the body cell of the male gametophyte. the pollen tube elongates and pierces and grows through the megasporangium wall and delivers the sperm cells to the female gametophyte inside. fertilisation takes place when the nucleus of one of the sperm cells enters the egg cell in the megagametophyte’s archegonium.
pollination