PTERIDOPHYTA – NEB Biology Notes

PTERIDOPHYTA Biology Notes Class 11

Pteridophyta are also called vascular cryptogams because among the cryptogams the vascular strands are present only in pteridophytes. They are most primitive among the vascular plants.

Division: Tracheophyta

Subdivision: Pteridophyta

Class: Pteropsida

Order: Pteridales

Family: Pteridaceae

Genus: Dryopteris

Fern are large group of highly advanced cryptogams. They are shade and moisture loving plants; grow abundantly in cool, shady and moist places of both in the hills and plains. Plant body of fern is sporophyte and differentiates into root, stem and leaves. Roots are adventitious arises from rhizome. The stem is mostly underground rhizome but sometimes it is erect and aerial, as in tree fern. Leaves are petiolate and pinnately compound. Young leaves are circinate (rolled from apex to downwards). The stem and petioles are covered with numerous brownish scales known as ramenta. Leaves are of two types: fertile (sporophyll) and sterile (trophophyll).

Reproduction of Fern        

Fern reproduces by all three methods: vegetative, asexual and sexual.

Vegetative reproduction: Vegetatively it reproduces by fragmentation, adventitious buds and apogamy. In fragmentation, rhizome breaks into fragments due to death and decay which later produce the new plants. Adventitious buds are formed at the point of attachment of leaf with rhizome.

On separation of these buds grow into new plant. Apogamy is the formation of new sporophyte directly from vegetative tissue of prothallus (gametophyte).

Asexual reproduction in Fern

Plant body is sporophyte. The spores are produced with in sporangia, which aggregate in groups called sori, formed on the surface and margin of leaves. These leaves are called sporophyll. The sporangium consists of multicellular stalk and a biconvex capsule. The capsule is composed of a single layer of thin walled cells stomium and highly thickened cells annulus. The spores are formed with in capsule by meiotic division of spores mother cells. When the spores mature the capsule brust at stomium. Then the spores germinate and gives rise the gametophytic structure i.e. prothallus.

Read this one too :   Zygomycetes - NEB Notes

Sexual reproduction in Fern

Prothallus of fern is monoecious. It is a heart shaped structure bears gametes and reproduce sexually. The undersurface of prothallus bears groups of highly differentiated reproductive organs antheridia and archegonia and unicellular hair like structure rhizoids. It shows the protandrous condition i.e. antheridium develops at first and then Archegonium. It shows the autotrophic mode of nutrition and act as independent gametophytic stage.

The antheridium is a spherical or oval body with many antherezoid mother cells in it. Each androcyte produce a single antherezoid. The Archegonium is a flask shaped body possesses narrow neck and swollen basal Venter. The venter possesses a single large egg cell.

On maturation antheridium brust and multicilliated antherezoid liberates. Fertilization takes place in the presence of water. Antherezoides enter into the venter through neck. They vibrate around ovum but only one of them fuses with egg nucleus. Thus fertilization occurs. The fertilized ovum secretes a wall and become oospore. The oospore is nourishing from the prothallus by rapid successive divisions the oospore develops into young embryo which forms the sporophyte. Prothallus decays and sporophyte develop into new plant of fern.

Alternation of generation in Fern

Fern plant is sporophyte (2n) and prothallus is gametophyte (n). The sporophyte reproduces asexually by spores and gives rise to gametophyte (prothallus). The prothallus reproduces sexually by fusion of male and female gametes and gives rise to sporophytic structure zygote. Thus two generations regularly alternate with each other in the life cycle of fern known as alternation of generation.

Economic importance:

  • Many ferns are grown as ornamental plants in the gardens for their large, showy and graceful foliage.
  • An antihelmintic drug is obtained from the rhizomes and petioles of the fern dryopteris.
  • The sporocarps of Marsilea are rich source of starch and used for their nutritive value.
  • Azolla is an aquatic fern used as biofertilizer.
  • Many species of ferns are edible.
Read this one too :   Evolution - Biology Notes Grade XI
Pteridophyta - Fern
Pteridophyta – Fern
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