It can withstand high temperatures and strong acids and alkali. No enzyme can degrade sporopollenin. Germ pores — apertures on exine where sporopollenin is absent — forms pollen tube. Pollen grains of large number of species are stored in liquid nitrogen at temperature — 0 , called pollen bank. Inside the ovary is ovarian cavity locule. The placenta is located inside the ovarian cavity.
Megasporangia ovules arise from placenta. Megasporogenesis- The process of formation of megaspore from megaspore mother cell by meiotic division is known as megasporogenesis. This process takes place in ovule. Ovule differentiates a single megaspore mother cell MMC in the micropylar region of nucellus. MMC undergoes meiotic division that results into the production of four megaspores. Two more sequential mitotic division results into 8-nucleate embryo sac.
At maturity ,embryosac is 8-nucleate and 7 celled. Cleistogamous — flower which do not open. Cleistogamous flowers produce assured seed-set even in the absence of pollinators. Geitonogamy is functionally cross-pollination involving a pollinating agent, genetically it is similar to autogamy since the pollen grains come from the same plant.
Agents of pollination includes abiotic water, wind and biotic insects, butterfly, honey bee etc. Water Pollination — Bryophytes, Pteridophytes, Algae. Main features of wind and water pollinated plants — produce pollen grains in large no. Insect Pollination — Flowers : large, colourful, fragrant, rich in nectar — Pollen grains : sticky — Stigma : sticky. Outbreeding Devices — the various mechanisms take discourage self-pollination and encourage cross pollination as continued self-pollination leads to inbreeding depression.
It includes. Pollen pistil interaction — the pistil has ability to recognize the compatible pollen to initiate post pollination events that leads to fertilisation. Pollen grain produce pollen tube through germ pores to facilitate transfer of male gametes to embryo sac.
Bagged flower- attains receptivity- mature pollen grains- dusted on the stigma — rebagged- fruits allowed to develop. Double Fertilisation- after entering the one of the synergids, each pollen grain releases two male gametes. One male gametes fuse with egg Syngamy and other male gametes fuse with two polar nuclei triple fusion to produce triploid primary endosperm nucleus PEN. Since two types of fusion takes place in an embryo sac the phenomenon is called double fertilisation.
The PEN develops into the endosperm and zygote develops into embryo. Post fertilisation events include endosperm and embryo development, maturation of ovules into seeds and ovary into fruits. Endosperm — the primary endosperm cell divides many time to forms triploid endosperm tissue having reserve food materials. Three cells are placed at the chalazal end. They are known as antipodals. At maturity, a typical angiosperm embryo sac has seven cells and eight nuclei.
Flowers in self-pollination are genetically similar. Self-pollination is of two kinds- autogamy and geitonogamy. Autogamy: The movement of pollen grains from the anther to the stigma of the same flower. It is preferred because of the following adaptations:. The stigma in Lilac is directly beneath the anthers.
Pisum, Lathyrus, and Commelina benghalensis are a few examples. Thus, self-pollination occurs during the bud stage of plants such as peas and wheat.
Geitonogamy is the transfer of pollen grain from one flower's anther to the stigma of another flower of the same or genetically similar plant. The benefits of self Pollination are shown below. Self-pollinated plants have a number of disadvantages as shown below. It is also referred to as allogamy.
Dicliny: Flowers are classified into two types: male and female. Plants could be either monoecious or dioecious. Dichogamy: It occurs when the anther and stigma mature at different times. For example, Salvia, Clerodendron, Sunflower, and Rose. Plantago, Magnolia, and Mirabilis are a few examples. Self-sterility: Tobacco and some crucifers, for example, have pollen grains that are incapable of growing over the stigma of the same flower. Prepotency refers to a pollen grain's ability to grow faster on the stigma of another plant than on the stigma of the same plant e.
Heterostyly: The styles and stamens are at different heights within the flowers. Primula and Jasminum have two types of flowers dimorphic heterostyly , pin-eye long style and short stamen and thrum-eye long style and short stamen short style and long stamens.
Some plants, such as Lathyrum and Oxalis, have trimorphic 3 heterostyly. Herkogamy: Self-pollination is prevented by the existence of a natural or physical barrier between androecium and gynoecium. Anemophily wind pollination Characteristics. They could have an air sac or wings.
Mulberry, Date palm, grass, coconut, willow, maize, jowar, cannabis are some examples. Hay fever is a kind of allergic reaction because of the presence of pollen in the air. Pollen grains lack exine and are frequently elongated. Vallisneria is a dioecious plant. Male plants produce a large number of male flowers, which after breaking rise upwards in a closed state and open on the water's surface. The female plant produces flowers that float on the surface of the water thanks to long pedicels.
After pollination, the female flower is submerged in water. Bees are drawn to bluish-purplish — violet — yellow flowers, while butterflies and wasps are drawn to reddish flowers. For instance, Bombax, Agave, Butea, and Bignonia. Myrmecophytes are plants that are pollinated by ants. Some members of the Rubiaceae family are examples. The germ tube secretes enzymes that digest the stigma tissues. The germ tube then develops into a pollen tube.
They are surrounded by cytoplasmic masses and appear as distinct male gametes. The pollen tube develops into the style tissues after passing through the stigma. They are as follows:. It then enters the synergids via the filiform apparatus. As a result, they are covered with a suitable-sized bag to prevent the deposition of unwanted pollen. The bag is generally made up of butter paper.
This process is called bagging. Two male gametes are released into the embryo sac by the pollen tube. The diploid zygote is formed when one of the male gametes fuses with the egg.
This is known as syngamy or generative fertilization. The second male gamete joins the two polar nuclei. This leads to the formation of a triploid primary endosperm nucleus.
This is known as triple fusion, and it is also referred to as vegetative fertilization. This is known as double fertilization. The endosperm is intended to nourish the embryo. It is typically triploid. The condition is known as xenia.
This happens because the endosperm in a mature ovule is fully developed. Focke described this effect. It is only found in Zea mays maize. Metaxenia is the action of pollen on the seed coat or pericarp that is outside the embryo sac. The endosperm is classified into three types based on how it develops. Nuclear endosperm. As an example, consider maize, wheat, and rice.
Cellular endosperm. As a result, the endosperm is cellular from the start, as in Datura, balsam, and Petunia. Helobial endosperm. Within these cells, the free nuclear division may occur. They may eventually become cellular as well. For example, Eremurus and Asphodelus. Coconut milk can also be used to induce embryo and plantlet differentiation from various plant tissues iv Zeatin is a highly effective cytokinin. It is derived from maize's young endosperm. As a result, embryo development is endoscopic.
It produces radicles. Vertically and once transversely to produce an embryo, which is a two-tiered eight-cell. Two cotyledons and a plumule are formed by the epibasal terminal tier. Only hypocotyls are produced by the hypobasal near the suspensor tier. Later, it takes on a heart shape before resuming its original shape. It comes to an end with the plumule, which is the tip of the stem. The plumule is the source of the future shoot.
It comes to an end at the root tip known as radical. The radicle is the source of the future root. The root cap is responsible for protecting the root tip. The curving of the ovule causes the cotyledons to curve as they emerge and elongate in Caspella bursa pastoris. In orchids such as Orboanche and Utricularis, the embryo does not differentiate into plumule, cotyledon, and radical.
It also produces a plumule and a large cotyledon. The plumule is pushed to one side as the cotyledon grows. The remnants of the second cotyledon are generally found in certain grasses. It is referred to as epiblast. The scutellum is the single cotyledon of monocots.
It has the shape of a shield and appears as a terminal. The hypocotyls and radicle are produced by the middle cell. It may result in an increase in suspensor cell numbers.
Both the radicle and the plumule are protected by sheaths. They are referred to as coleorhizae and coleoptiles, respectively. They could be scutellum extensions. Fruit refers to a ripened or fertilized ovary. The pericarp is a fleshy or dry fruit wall formed by the ovary wall. Epicarp, mesocarp, and endocarp are the three layers of fleshy fruit or pericarp. It is the fruit covering that develops from the ovary wall.
The testa is formed by the outer integuments, and the tegmen is formed by the inner integuments. It adds a layer of seed protection. It's referred to as caruncle. It aids seed germination by absorbing water.
Because they are the lightest in the plant kingdom, they are known as dust seeds. Each orchid seed weighs approximately Gram, pea, bean, and orchid are some examples. The cotyledons are thin in this case. Wheat seed, barley seed, castor seed, poppy seed, and so on are examples.
It shields the embryo from harm. Phoenix dactylifera seeds discovered in King Herod's palace near the Dead Sea years ago have been found to be viable. It occurs through the following mechanisms:. Parthenos — virgin; genesis — descent. It goes through parthenogenesis and produces a diploid embryo.
Apo — without, gamos — marriage.
0コメント