Reproduction In Flowering Plants of Class 12
Definition : Reproduction is the process of formation of new individuals from pre-existing ones and is a mean of perpetuation of race as the older individuals undergo senescence and die. Reproduction is meant for perpetuation of a species because individuals are bound to die after a fixed life span.
Reproduction is of two types:
- Asexual (Apomixis)
Asexual (or Apomixis, Gk. apo—without, mixis—marriage)
It is formation of new individuals without involving formation and fusion of gametes.There is no meiosis and syngamy, so no gene recombination. Hence it produces genetically identical individuals.
Types: It takes place by three methods—agamospermy, spores formation and vegetative propagation.
Agamospermy (Gk. agamos—without marriage, sperma—seed)
It is formation of seed without the formation and fusion of male and female gametes. It can take place by following three methods:
- Adventitive Embryony: It is the formation of diploid embryo from cells, other than egg cell.It involves direct development from cells of nucellus or integument of the ovule (megasporangium). These are called as nucellar or integumental embryos. e.g., Citrus, Opuntia and mango.
Recurrent Agamospermy (Recurrent Apomixis): Diploid egg (or oosphere) grows parthenogenetically into diploid embryo, e.g., Apple, Allium, Poa. It takes place by :
- Apospory. Diploid embryo sac develops from diploid nucellar cell.
- Diplospory. Diploid embryo sac develops directly from diploid megaspore mother cell.
- Non-Recurrent Agamospermy. Haploid embryo develops parthenogenetically from haploid egg. e.g. Banana.
They are single celled dissemules which can be produced by mitosis (mitospores) or meiosis (meiospores). On germination, they give rise to a new plants. These spores are conidia, oidia, chlamydospores, endospores, pycnidiospores, zoospores, ascospores, basidiospores, uredospores, teleutospores, aecidiospores, aplanospores, hypnospores etc. e.g., Monera, Protista, Fungi, Algae, etc.
It is the formation of new plants from a piece/fragment/detached vegetative part of the plant. It is recorded in case of lower plants as well as higher plants.
Lower Plants. Vegetative propagation in lower plants takes place by:
- Binary Fission. e.g., bacteria, diatoms, Euglena.
- Budding. e.g., Yeast.
- Fragmentation. e.g., Marchantia, Spirogyra, Nostoc.
- Gemmae. e.g., Funaria, Marchantia.
Higher Plants. Vegetative propagation in higher plants takes place by :
- Roots. Tap root branches can develop adventitious buds and form new plants, e.g., Dalbergia (Sheesham), Guava, Poplar, Albizia, Murraya. Fleshy roots (root tubers) which develop adventitious buds also take part in vegetative propagation, e.g., Sweet Potato, Tapioca, Dahlia, Asparagus.
Underground Stems. All types of underground stem structures can take part in vegetative propagation.
- Stem Tubers. They form new plants in the region of nodes or eyes, e.g., Artichoke, Potato.
- Bulb. Buds present inside bulbs sprout to from new plants, e.g., Garlic, Narcissus, Onion.
- Corm. It is unbranched, swollen structure which bears many buds for growth of new plants, e.g., Amorphophallus, Colacasia, Crocus, Freesia.
- Rhizomes. Rhizomes take part in vegetative propagation due to presence of buds, e.g., Banana, Ginger, Turmeric, Adiantum.
- Suckers. They are slender underground branches which develop from base of aerial shoot. Breaking of suckers form independent plants, e.g., Mint, Chrysanthemum.
Subaerial Stems. There are three types of subaerial stem structures which take part in vegetative propagation.
- Runners. They are special, narrow, green, horizontal branches which develop at the base of crown and root at intervals where new crowns are also formed. e.g., Lawn grass, Centella, Mint.
- Stolons. They are special arched above ground horizontal branches which develop at the base of a crown and help in vegetativepropagation, e.g., Strawberry.
- Offsets. They are one internode long runners which occur in some aquatic plants. e.g., Eichhornia (Water Hyacinth), Pistia (Water Lettuce).
- Aerial Shoots. Segments of Opuntia and other Cacti produce new plants after falling on ground.
- Leaves. Leaves of many plants having adventitious buds, help in vegetative propagation, e.g., Begonia, Bryophyllum, Adiantum caudatum.
- Bulbils. Bulbils are fleshy buds which take part in vegetative propagation, e.g., Oxalis, Agave, Pineapple, Dioscorea, Lily, Chlorophyllum.
- Turions. These are fleshy buds which develop in aquatic plants for propagation as well as perennation, e.g., Potamogeton, Utricularia.