Ovule

-
Ovule, in botany, is the name applied to immature seeds, which are produced within the ovary of a flower. In flowering plants, the development of the ovule is generally as follows.

At the site of the future seed, an outgrowth, the nucellus or megasporangium, develops; this becomes covered by two integuments that grow up from its base, leaving an opening at the top called the micropyle. Within the nucellus is the megaspore mother cell. It divides into two and then into four; one of these megaspores then typically divides into eight nuclei to become the embryo sac of the female gametophyte. It is in this sac that the plant embryo will develop.

The young male plants, or male gametophytes, are popularly referred to as pollen grains; these are contained in modified leaves called stamens. When a pollen grain is placed on the stifma, it sends out a tube that grows down to the ovary and eventually enters the ovule. Two sperms are then discharged into the embryo sac; one of these fuses with the egg nucleus at the micropylar end of the embryo sac, and this fertilized egg then develops into the embryo of the seed. The other sperm fuses with two nuclei near the middle of the embryo sac; the resulting triple-fusion nucleus develops into the endosperm, which usually remains as the food storage tissue of the seed.

See Fertilization; Flower; Pollination.

Comments

Post a Comment

Popular posts from this blog

Plant: Cell Structure And Function

-
Image
Plant Cell Plant cells contain a variety of membrane-bound structures called organelles. These include a nucleus that carries genetic material; mitochondria that generate energy; ribosomes and rough endoplasmic reticulum that manufacture proteins; smooth endoplasmic reticulum that manufactures lipids used for making membranes and storing energy; and a thin lipid membrane that surrounds the cell. Plant cells also contain chloroplasts that capture energy from sunlight and a single fluid-filled vacuole that stores compounds and helps in plant growth. Plant cells are surrounded by a rigid cell wall that protects the cell and maintains its shape. The tremendous variety of plant species is, in part, a reflection of the many distinct cell types that make up individual plants. Fundamental similarities exist among all these cell types, however, and these similarities indicate the common origin and the interrelationships of the different plant species. Each individual plant cell is at
Read more

Monocot and Dicot Seeds

-
Image
Monocotyledons (monocots) and dicotyledons (dicots) make up the two large groups of flowering plants, differentiated by their seed structures. Monocot seeds contain one cotyledon, or embryonic leaf. When these seeds germinate, the cotyledon remains below ground, absorbing nutrients from the endosperm, the starchy food supply in the seed. The coytledon transports these nutrients to the developing seedling. Dicot seeds contain two coytledons, which absorb and store the nutrients from the endosperm before the seed germinates. The cotyledons, thick with stored nutrients, emerge above ground during germination, and then transport the stored nutrients to the developing seedling. For a brief time, the cotyledons also serve as the first photosynthesizing leaves, but they wither and die when the true leaves emerge. related articles: flower flower variations in structure flower sexual reproduction flower pollination and fertilization flowering and the life cycle evolution of flowers angios
Read more

Insectivorous Plants

-
Image
Insectivorous Plants, also carnivorous plants, plants that gain some of their nutrition from animals, especially insects, captured by the plants themselves. Most occur in bogs where the soil is acid and poor in available nitrogen; capturing insects is one way of getting nitrogenous compounds without manufacturing them. At the same time, the green leaves of these plants manufacture carbohydrates. The trapping mechanism of insectivorous plants is relatively small. Therefore, prey is almost inevitably limited to small insects. Insectivorous plants are diverse and represent members of three orders of dicots : Nepenthales, Scrophulariales, and Rosales. A majority are in the Nepenthales, including the pitcher plant , sundews and the Venus's-flytrap, and East Indian pitcher plants. Others include the bladderworts, butterworts, and the Australian pitcher plant. Discussed below are the sundews and bladderworts. Certain species of fungus are known to be carnivorous as well. Venus’s-Flytrap
Read more