17 June 2021

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GENERAL CHARACTERS OF GYMNOSPERM

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GENERAL CHARACTERS :

Gymnos: Naked
Sperma: Seeds

  1. The plants shows alternation of generation. The gametophyte and sporophyte phases alternate with each other to complete the life cycle.
    (a) Gametophytic Phase: It is subsidiary phase which is haploid and short lived.
    (b) Sporophytic Phase: It is main phase which is diploid, long lived and occurs as a whole plant.
  2. Plants of this group possess naked ovule/seeds.
  3. Ovules are naked and not enclosed by the ovary therefore recognized as a Gymnosperm.
  4. Gymnosperms vary in size from small plants to very large gigantic plants.
    Zamia pygmea is the smallest Gymnosperm having an underground tuberous stem (20-30 cm).
    Sequoia sempervirens is the tallest tree of the world having height of about 150 m.
  5. Plant body is Sporophytic and differentiated into root, stem and leaves.
  6. Leaves are two types-
    (a) Foliage leaves (Big and Green)
    (b) Scaly leaves (Minute and Brown)
  7. The leaves may be simple or compound.
  8. Leaves having thick cuticles and sunken stomata.
  9. Plants are evergreen, perennial trees or shrubs showing xerophytic characters.
  10. Vascular tissues are present.
  11. Absence of true vessels and companion cells.
  12. The stems are unbranched (Cycas) or branched (Pinus, Cedrus).
  13. Gymnosperms show single fertilization.
  14. Pollination takes place through wind and formation of endosperm takes place before fertilization (pre-fertilized).
  15. The ovules are Orthotropous.
  16. True fruits are lacking because of the absence of ovary.
  17. Sporophylls are arranged on central axis in the form of cone or strobilus.
  18. Cones are unisexual and Gymnosperm are heterosporous.
  19. In a male cone, microsporophylls bear microsporangia which produce a large number of microspores and in female cone, megasporophyll bears megasporangia which produce four megaspores.
    Note: At this point microsporophyll, microsporangia and microspores can be compared with stamen, anther and pollen grains of Angiosperms respectively. Similarly megasporophyll and megasporangia can be compared with gynoecium and ovule respectively.
  20. The roots are generally tap roots. Roots in some genera have fungal association in the form of mycorrhiza (Pinus). In other genera, specialised roots called coralloid roots (associated with N2-fixing Cyanobacteria in Cycas).

Eg.: Cycas, Pinus, Thuja (ornamental plant in gardan- Morpichh or Vidhya), Araucaria (Christmas tree), Bennettites (Fossil plant).

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