Gametophyte thallus may reproduce by vegetative
and sexual method.
Vegetative reproduction:
a)
Gemma:
Gemmae are the multicellular, flat, green vegetative bodies developed on the
stem apex, leaf apex or sometimes on the rhizoids. After detachment from the
parent body, it germinates to new gametophyte thallus.
a)
Primary and secondary protonema: Main primary protonema may be branched, detached
and form new thallus. Sometimes secondary protonema may also be developed from
different part of the gametophyte and these secondary protonema develop into
new thallus at favourable condition.
Sexual reproduction:
Thallus
of Funaria is monoecious and autoecious (antheridia and archegonia develop on two
different branches of the same
gametophyte plant.). Reproductive bodies ie. antheridia and archegonia develop
in groups at the apex of the respective male and female branches of the same gametophore.
Here the male branch grow first and later on female branch develops at the base
of the lateral position of the male
branch.
Antheridia:
The male reproductive organ ie. antheridia
(singular- antheridium) develop in culture at the apical position of the male
branch. At the tip along with antheridia a number of intermediate sterile,
multicellular, uniceriate, chloroplast bearing filaments or hairs are also
found known as paraphyses. The terminal cells of these paraphyses are swollen. Surrounding
the antheridia and paraphyses, vegetative leaves aggregate in a rosette form,
known as perigonial leaves.
A single antheridium is composed of a basal multicellular
stalk, on the stalk a globose, club shaped body is present. The body is
protected by an outer single cell layer thick jacket. At immature condition the
cells of the jacket have lot of chloroplast but with maturity chloroplast has
been lost. At the terminal of the antheridium 2-3 celled large colour less operculum
cells are also found. Inside the jacket a mass of numerous androcyte or sperm
mother cells are present.
At maturity in availability of water the operculum
cells rupture and forms a minute opening in the antheridium tip, through this
opening the mass of androcyte comes out and become available at the perigonial cup.
Each androcyte now metamorphoses into a single antherozoid with interaction of
water. A single antherozoid is an elongated biflagellate in structure.
Archegonia:
As like antheridia, archegonia are also grown
at the top of female branch in clusters along with paraphyses. Here the
paraphyses are not swollen at their tip. Vegetative leaves are also aggregate
at the surrounding of the archegonia and paraphyses but here they are known as
perichaetial leaves.
A single archegonium has a short multicellular
jacket, a basal swollen venter and a slender, elongated neck. The jacket of the
archegonium is single layered at the neck (6 rows of cells present) whereas at
the venter is two celled thick. The neck has 5-6 neck canal cells and venter
has one apical ventral canal cell and a basal large egg. At the terminal end of
the neck, cover cells are present that closing the neck.
Fertilization:
At maturity archegonium losses the cover
cells and in presence of water the neck canal cells and ventral canal cell disintegrate
and form a mucilaginous matrix. By the help of water (source: rain or dew) antherozoids
reach to the neck tip of archegonium. Antherozoid passes through the matrix formed
inside the neck and finally reaches to the venter. Inside the venter the antherozoid
finally fuses with the egg and thus fertilization takes place. As a result of fertilization,
a diploid zygote is formed inside the venter.
No comments:
Post a Comment