Sexual Reproduction in Flowering Plants

Vocabulary flashcards covering the biological processes, structures, and key botanical figures involved in the sexual reproduction of flowering plants.

Panchanan Maheshwari

A distinguished Indian botanist (1904-1966) who popularized the use of embryological characters in taxonomy and established the Department of Botany at the University of Delhi.

Floriculture

The cultivation and study of flowers, which are considered objects of aesthetic, ornamental, social, religious, and cultural value.

Androecium

The male reproductive organ of a flower consisting of a whorl of stamens.

Gynoecium

The female reproductive organ of a flower representing the pistil or whorl of pistils.

Stamen

The male reproductive unit consisting of two parts: the long and slender stalk called the filament and the terminal bilobed structure called the anther.

Dithecous

A characteristic of an angiosperm anther having two lobes, where each lobe has two theca separated by a longitudinal groove.

Microsporangia

Four structures located at the corners of a tetragonal anther that develop further into pollen sacs.

Tapetum

The innermost wall layer of the microsporangium that nourishes the developing pollen grains and possesses dense cytoplasm with more than one nucleus.

Sporogenous tissue

A group of compactly arranged homogenous cells occupying the center of each microsporangium when the anther is young.

Microsporogenesis

The process of formation of microspores from a pollen mother cell (PMC) through meiosis.

Pollen grains

The structures representing the male gametophytes, generally spherical and measuring about $25-50$ micrometers in diameter.

Exine

The hard outer layer of a pollen grain made up of sporopollenin, one of the most resistant organic materials known.

Sporopollenin

A highly resistant organic material that can withstand high temperatures and strong acids and alkali, found in the exine of pollen grains.

Germ pores

Apertures in the pollen grain exine where sporopollenin is absent and through which the pollen tube emerges.

Intine

The thin and continuous inner wall of the pollen grain made up of cellulose and pectin.

Vegetative cell

The larger of the two cells in a mature pollen grain which has abundant food reserve and a large irregularly shaped nucleus.

Generative cell

The smaller spindle-shaped cell that floats in the cytoplasm of the vegetative cell and divides to form two male gametes.

Parthenium

Commonly known as carrot grass, it is a contaminant that came into India with imported wheat and causes pollen allergy.

Pollen banks

Facilities where pollen grains are stored for years in liquid nitrogen at $-196^{\circ}C$ for use in crop breeding programmes.

Monocarpellary

A gynoecium consisting of a single pistil.

Multicarpellary

A gynoecium consisting of more than one pistil.

Syncarpous

A condition where multiple pistils in a flower are fused together, as seen in Papaver.

Apocarpous

A condition where multiple pistils in a flower are free, as seen in Michelia.

Megasporangia

Commonly called ovules, these are structures arising from the placenta inside the ovary.

Funicle

The stalk by which an ovule is attached to the placenta.

Hilum

The region representing the junction between the ovule and the funicle.

Micropyle

A small opening at the tip of the ovule where the integuments do not encircle the nucellus.

Chalaza

The basal part of the ovule located opposite the micropylar end.

Nucellus

A mass of cells enclosed within the integuments that contains abundant reserve food materials.

Megasporogenesis

The process of formation of megaspores from the megaspore mother cell (MMC) via meiosis.

Monosporic development

The formation of an embryo sac from a single functional megaspore while the other three degenerate.

Filiform apparatus

Special cellular thickenings at the micropylar tip of synergids that guide the pollen tube into the synergid.

Egg apparatus

A group of three cells at the micropylar end of the embryo sac consisting of two synergids and one egg cell.

Pollination

The mechanism of transfer of pollen grains from the anther to the stigma of a pistil.

Autogamy

The transfer of pollen grains from the anther to the stigma of the same flower.

Cleistogamous flowers

Flowers that do not open at all, ensuring autogamy and seed-set even in the absence of pollinators.

Geitonogamy

The transfer of pollen grains from the anther to the stigma of another flower of the same plant; genetically similar to autogamy.

Xenogamy

The transfer of pollen grains from the anther to the stigma of a different plant, bringing genetically different types of pollen.

Inbreeding depression

A condition resulting from continued self-pollination that flowering plants avoid through various outbreeding devices.

Self-incompatibility

A genetic mechanism that prevents self-pollen from fertilising the ovules by inhibiting pollen germination or tube growth.

Pollen-pistil interaction

The dynamic process involving pollen recognition followed by promotion or inhibition, encompassing all events from pollen deposition to entry into the ovule.

Emasculation

The removal of anthers from a bisexual flower bud before they dehisce using a pair of forceps in artificial hybridisation.

Double fertilisation

An event unique to flowering plants involving both syngamy (to form a zygote) and triple fusion (to form a primary endosperm nucleus).

Triple fusion

The fusion of one male gamete with two polar nuclei to produce a triploid primary endosperm nucleus (PEN).

Scutellum

The single cotyledon found in the grass family, situated laterally to the embryonal axis.

Perisperm

The residual, persistent nucellus found in certain mature seeds like black pepper and beet.

Dormancy

A state of inactivity entered by an embryo when seeds mature and become relatively dry.

False fruits

Fruits where the thalamus contributes to formation alongside the ovary, such as apple, strawberry, and cashew.

Parthenocarpic fruits

Fruits that develop without fertilisation and are usually seedless, such as bananas.

Apomixis

A form of asexual reproduction that mimics sexual reproduction by producing seeds without fertilisation.

Polyembryony

The occurrence of more than one embryo in a single seed, common in Citrus and mango.