Lesson 12 of 12 · 13 min
Chapter review
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Must-know facts
20 facts
- 01A typical anther is bilobed, dithecous and tetrasporangiate: four microsporangia, two per lobe.
- 02Microsporangium wall, outside to inside: epidermis, endothecium, middle layers, tapetum; the tapetum nourishes the pollen and its cells are often multinucleate.
- 03Exine is sporopollenin, absent only at germ pores; intine is cellulose and pectin.
- 04Over 60 per cent of angiosperms shed pollen at the 2-celled stage (vegetative + generative cell).
- 05Rice and wheat pollen lose viability within 30 minutes; pollen is stored in liquid nitrogen at −196 °C.
- 06Parthenium (carrot grass) came to India with imported wheat and causes pollen allergy.
- 07Hilum joins ovule to funicle; micropyle is at the tip; chalaza at the base; nucellus holds the embryo sac.
- 08One megaspore functions (monosporic); three free-nuclear mitoses give 8 nuclei; embryo sac is 7-celled, 8-nucleate.
- 09Egg apparatus = 2 synergids + 1 egg, at the micropylar end; filiform apparatus of synergids guides the pollen tube.
- 10Cleistogamous flowers (Viola, Oxalis, Commelina) are always autogamous.
- 11Geitonogamy is functionally cross-pollination but genetically autogamy; only xenogamy brings genetically different pollen.
- 12Water pollination: about 30 genera, mostly monocots; Vallisneria, Hydrilla, Zostera. Water hyacinth and water lily are not water-pollinated.
- 13Monoecy (castor, maize) prevents autogamy only; dioecy (papaya) prevents autogamy and geitonogamy.
- 14Syngamy gives a 2n zygote; triple fusion gives a 3n PEN; together they are double fertilisation.
- 15Coconut water is free-nuclear endosperm; the kernel is cellular endosperm.
- 16Albuminous: wheat, maize, barley, castor. Non-albuminous: pea, groundnut. Perisperm: black pepper, beet.
- 17Mature seeds hold 10-15 per cent moisture; the ovary wall becomes the pericarp.
- 18False fruits: apple, strawberry, cashew (thalamus contributes). Parthenocarpy: banana.
- 19Lupinus arcticus seed germinated after about 10,000 years; Phoenix dactylifera seed about 2000 years old.
- 20Nucellar polyembryony in Citrus and mango; apomixis in some Asteraceae and grasses.
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Key terms
18 terms
- Dithecous
- Of an anther lobe or anther with two thecae per lobe, as in a typical angiosperm anther.
- Tapetum
- Innermost wall layer of the microsporangium; it feeds the developing pollen and has dense, often multinucleate cells.
- Microsporogenesis
- Formation of four haploid microspores from a pollen mother cell by meiosis.
- Sporopollenin
- The highly resistant material of the exine, broken down by no known enzyme.
- Germ pore
- A gap in the exine without sporopollenin, through which the pollen tube emerges.
- Nucellus
- Food-rich tissue of the ovule, inside the integuments, that contains the embryo sac.
- Monosporic development
- Formation of the embryo sac from just one of the four megaspores.
- Filiform apparatus
- Thickenings at the micropylar tip of the synergids that guide the pollen tube in.
- Cleistogamy
- Bearing flowers that never open, so pollination is always within the flower.
- Geitonogamy
- Transfer of pollen to another flower on the same plant.
- Xenogamy
- Transfer of pollen to the stigma of a flower on a different plant.
- Self-incompatibility
- A genetic block on germination or tube growth of pollen from the same plant.
- Emasculation
- Removing anthers from a bisexual bud before they dehisce, in artificial crossing.
- Triple fusion
- Fusion of one male gamete with the two polar nuclei, giving the 3n primary endosperm nucleus.
- Scutellum
- The single, laterally placed cotyledon of a grass embryo.
- Perisperm
- Persistent remains of the nucellus in a seed, as in black pepper and beet.
- Parthenocarpy
- Development of a fruit without fertilisation, giving a seedless fruit such as banana.
- Polyembryony
- Presence of more than one embryo in a seed, as in Citrus.