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nucellus
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nucellus

plant anatomy

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  • development of seed and fruit
    • magnolia fruit and seeds
      In seed: Angiosperm seeds

      …part a region called the nucellus that in turn contains an embryo sac with eight nuclei, each with one set of chromosomes (i.e., they are haploid nuclei). The two nuclei near the centre are referred to as polar nuclei; the egg cell, or oosphere, is situated near the micropylar (“open”)…

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role in

    • angiosperm megagametogenesis
      • snake gourd flower
        In angiosperm: Ovules

        This megasporangium is called the nucellus in angiosperms. After initiation of the carpel wall, one or two integuments arise near the base of the ovule primordium, grow in a rimlike fashion, and enclose the nucellus, leaving only a small opening called the micropyle at the top. In angiosperms the presence…

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    • conifer embryogenesis
      • fern life cycle
        In plant development: Nutritional dependence of the embryo

        …within the tissues of the nucellus and acquires abundant food reserves. The proembryo forms after a period of free-nuclear division in the zygote, and the tier of cells above the basal four then elongates to form a suspensor, which pushes the embryonic group deep into the gametophyte. Secondary suspensor cells…

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    pistil
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    pistil and stamens how flowering plants reproduce passion flower Rose of Sharon (Hypericum calycinum) flower parts flower anatomy floral diagrams Cross-pollination floral diagram Self-pollination
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    pistil and stamens
    pistil and stamens A lily flower with a central pistil surrounded by stamens. The six orange structures are pollen-laden anthers, each borne at the end of a stalk known as a filament.

    pistil

    plant anatomy
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    Article History
    how flowering plants reproduce
    1 of 2
    how flowering plants reproduceReproduction in flowering plants begins with pollination, the transfer of pollen from anther to stigma on the same flower or to the stigma of another flower on the same plant (self-pollination) or from the anther on one plant to the stigma of another plant (cross-pollination). Once the pollen grain lodges on the stigma, a pollen tube grows from the pollen grain to an ovule. Two sperm nuclei then pass through the pollen tube. One of them unites with the egg nucleus and produces a zygote. The other sperm nucleus unites with two polar nuclei to produce an endosperm nucleus. The fertilized ovule develops into a seed.
    passion flower
    2 of 2
    passion flowerPassion flower blossom (Passiflora), showing the circle of five sepals and five petals; the fringelike corona; the five stamens, each with a loaf-of-bread-shaped anther; the ovary; and the three styles.

    pistil, the female reproductive part of a flower. The pistil, centrally located, typically consists of a swollen base, the ovary, which contains the potential seeds, or ovules; a stalk, or style, arising from the ovary; and a pollen-receptive tip, the stigma, variously shaped and often sticky. In pollination, compatible pollen grains land on the stigma and then germinate, forming a pollen tube. The pollen tube grows down through the tissue of the style to deposit sperm for the fertilization of the ovules in the ovary. Pistils in the collective sense form the gynoecium, in distinction to the male reproductive parts, or androecium (see stamen).

    Each pistil is constructed of from one to many enrolled leaflike structures, or carpels, each of which encloses one or more ovules. The carpel is a single megasporophyll, or modified seed-bearing leaf. A pistil then may be composed of one carpel (simple pistil), as in the sweet pea, or of two or more carpels (compound pistil) partially or completely joined, as in the mustard (two carpels) or lily (three carpels). A flower that contains separate pistils (and therefore separate carpels) is termed apocarpous. If it contains a single pistil with two or more united carpels, it is syncarpous.

    Rose of Sharon (Hypericum calycinum)
    Rose of Sharon (Hypericum calycinum)

    Differences in the composition and form of the pistil are useful in determining taxonomic relationships. There may be a single pistil, as in the lily, or several to many pistils, as in the buttercup. The lobes of the stigma are often characteristic of families or genera; for example, many bellflowers (Campanula) have a distinctive stigma with three curling lobes.

    This article was most recently revised and updated by Melissa Petruzzello.
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