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Gymnosperms
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Gymnosperms
Belong to the group Phanerogams i.e., seed bearing plants. They have naked seeds (not enclosed within a fruit). They are mainly xerophytes.
Have diplontic life cycle.
Plant body is the sporophyte & the gametophytic generation is very much reduced.
Sporophyte is well differentiated into root, stem & leaves.
Roots: Tap root system.
Stem: Thick, woody with scars of fallen leaves.
Leaves are 2 types: foliage leaves & scale leaves.
They are either monoecious or dioecious.
Secondary growth occurs.
They are heterosporous and bear male & female cones.
MALE REPRODUCTIVE PART:
Male cones are smaller in size & short lived.
They consist of spirally arranged microsporophylls.
Microsporophyll bear microsporangia inside which the microspores/pollens are produced after meiosis.
Pollen/microspore starts dividing in the microsporangium.
They produce 1-2 prothallial cells, a generative cell & a tube cell.
Further development occurs after pollination.
The generative cell divides to form body cell & stalk cell. The body cell then produces 2 male gametes. Tube cell forms the pollen tube carrying the male gametes.
FEMALE REPRODUCTIVE PART:
Female cones are larger in size.
They consist of spirally arranged megasporophylls.
Megasporophyll bear megasporangia.
Megasporangia/ovule is orthotropous type.
Inside ovule develops megaspore mother cell that undergoes meiosis to form 4 megaspores, 3 of which degenerate.
The 4th functional megaspore forms the female gametophyte, that possesses 2-8 archegonia. Egg are produced in archegonia.
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Pollination is anemophilous.
Fertilization occurs in archegonia.
Development of embryo is meroblastic.
The zygote divides to form the embryo having cotyledons, plumule & radicle.
Polyembryony occurs.
Ovule matures into seed & the female gametophyte forms the endosperm.
Divided into 4 classes:
Coniferopsida: e.g., Pinus, Abies, Cedrus.
Cycadopsida: e.g., Cycas, Zamia.
Ginkgopsida: e.g., Ginkgo.
Gnetopsida: e.g., Gnetum, Ephedra, Welwitschia.
PINUS:
Mycorrhizal roots occur.
Stem shows monopodial branching.
Simple, needle-shaped leaves.
Monoecious.
2 microsporangia per microsporophyll.
Pollens possess 2 air sacs that act as wings.
Many cotyledons present.
pycnoxylic wood(densely packed).
CYCAS:
Coralloid roots occur.
Unbranched stem with a crown of leaves.
Leaves are pinnately compound.
Dioecious.
Microsporangia develop in groups called sori in the microsporophylls.
Female cone is not formed. Megasporophylls lie scattered.
Two cotyledons present.
They possess largest egg, sperm & ovule.
Wood is manoxylic (not compact).
Also Read Bryophyta and Alteration of generation.
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