Sexual Reproduction in Plants

The pollen grains having a single furrow are known as monocolpate.The pollen grains of monocots also differ from those of most dicots. In monocots, each pollen grain has just one thin-walled region, the colpus, which is the area from which the pollen tube emerges when the pollen grain germinates.

Sporopollenin is a major component of the tough outer (exine) walls of spores and pollen grains. It is chemically very stable and is usually well preserved in soils and sediments.

The megasporangium is surrounded by layers of sporophyte tissue called the integument. The integument and structures within i.e.,megasporangium and megaspore are called the ovule.

In this type, the ovary is monolocular. The ovules are few or reduced to one and borne at the base of the ovary. The ovule when solitary often fills the ovary cavity e.g., sunflower.

In this type, the ovule takes a 90 degree turn so that the micropyle is at right angles to the funicle.

In this type, the ovary has two or more carpels, syncarpous and has two or more locules. The ovules are borne at or near the centre on the axis formed by the union and fusion of the septa (partitions) and usually in vertical rows e.g., apple, hibiscus etc..

This cell forms the sperm cells that fertilize the egg in the flower. In the loculi of the anthers, cells produce pollen mother cells. They undergo the process of mitosis to form sperm cells: each mother cell creates four sperm cells. The original germ cell divides into two sperm cells. This split can occur before or after the grain reaches the stigma, depending on the species.

Ovaries are attached directly to the receptacle, but can be sunken into it superior with no stalk, or on stalk-like extensions of the receptacle, as in Isomeris arborea. The ovary surrounds one or more locules in which ovules develop from placenta.

The Rosaceae or rose family is a large family of flowering plants, Roses can be herbs, shrubs or trees. Most species are deciduous, but some are evergreen.They have a worldwide range, are the most diverse in the northern hemisphere. The flowers have superior ovaries.

If a gynoecium has multiple carpels fused into a single structure, it is syncarpous. A syncarpous gynoecium can sometimes appear very much like a monocarpous gynoecium.

It is the outermost whorl consisting of units called sepals.These are typically green and enclose the rest of the flower in the bud stage, however, they can be absent or prominent and petal-like in some species.

It is stalk or the basel barren part of a flower. A flower with pedicel is called pedicellate, e.g., Hibiscus, Caesalpinia and without pedicel is called sessile, e.g., Polianthes, disc floret of Helianthus.

It is the second whorl internal; to die calyx. It is made up of petals which are usually enlarged, delicate, bright coloured and often with sweet fragrance. Their function is to attract insects for pollination and also to protect the inner essential whorls.

The flowers are not scented as birds have good vision but poor sense of smell.

Insects also visit flowers for their nectar. Nectar is secreted by specialized areas called nectaries, which vary in position from flower to flower. Butterflies and moths feed exclusively on nectar. They possess sucking mouth parts (proboscis). The length of the proboscis has always a relationship to the flower visited. Insects with long proboscis visit flowers with deep tubular corollas.

Pollen grains are light, dry and non-sticky.  In some plants the pollen grains are even winged, so that they are easily carried by the wind.

Some plants never open their flowers to ensure complete self-pollination. This condition is called Cleistogamy, e.g., Commelina bengalensis, Oxalis, Viola, etc., The cleistogamous flowers are bisexual small, inconspicuous, colourless and do not secrete nectar.

Anthers and stigma of the bisexual flowers of some plants mature before the opening of the buds to ensure self-pollination, (e.g.,) Wheat, Rice, Pea, etc..

The plants have well developed conducting tissues, the xylem has xylem vessels and the phloem has sieve tubes and companion cells. The xylem and phloem are arranged in the form of vascular bundles.

It is not economical. Plants waste a lot of energy and food materials in unnecessary adaptations and devices to bring about pollination. It is uncertain because a factor of chance is always involved.

In some plants, when the mature pollen falls on the receptive stigma of the same flower, it fails to bring about self-pollination. It is called self-incompatibility. Under such conditions, cross-pollination is the only option.

The genus Salvia belongs to family Labiatae (Mint family) in which the gamopetalous corolla is two-lipped (Bilabiate). The lower lip provides platform for the visiting insect and the upper lip is just like a hood which protects the floral organs. The flowers are protandrous. Each flower has two epipetalous stamens located in anterio-lateral position.It is an entomophilus flower.

Ornithophily is a mode of pollination performed by birds The act of pollination is not performed by all the birds except a few. The most common bird pollinators are Sun bird, Humming bird, Crow, Bulbul, Parrot, Mynah etc..

Bats bring about pollination only in the tropics. Bats are nocturnal animals and the flowers they visit are large and emit a strong odour. They move very fast and transport pollen to long distances. Bat pollinated flowers generally produce more nectar than ornithophilous flowers. They also have a large number of stamens.

Fourth whorl (female organ of the flower) consists of carpel or megasporophylls. The pistil consists of Fourth whorl (female organ of the flower) consists of carpel or megasporophylls. The pistil consists of ovary, style and stigma.The ovary contains one or more round or oval ovules (rudimentary seeds). Each ovule encloses embryo sac.