In Dryopteris, reproduction takes place by three methods i.e. vegetative method, asexual method, and sexual method.
It takes place by death and decay of older parts of rhizome up to the branch.
Reproduction by spore formation
Dryopteris is homosporous. Spores are produced in the sporangium. Sporangia are aggregated together and form sorus. Sori are found on the lower surface of pinnule in each vein. Sporangium develops from the swollen placenta. Sorus is covered with kidney shaped protective covering known as indusium.
Structure of sporangium
It is oval or biconvex structure. It has two parts i.e. multicellular stalk and capsule. The sporangial wall is single layered which has two regions i.e. annulus and stomium. The annulus is thick walled and stomium is thin walled. There is the presence of diploid spore mother cells inside the sporangium. spore mother cells divide meiotically and produce haploid spores. There are 32 to 64 spores produced in a sporangium.
The annulus is hygroscopic in nature. The outer thin wall of annulus evaporates water after maturation of sporangium during dry environment, due to which annulus contract and there is the splitting of the sporangial wall from stomium. Spores come out of the ruptured sporangial wall. Spores are dusty in nature. Spore is uninucleate haploid spherical structure.
Spore germinates into gametophyte known as prothallus. Prothallus is green, independent, artificially heart shaped, monoecious having male and female reproductive organs antheridia and archegonia respectively. Archegonia are found towards the apical notch and antheridia are found towards the basal region in the ventral surface. Rhizoids are also found in the basal region of prothallus.
Archegonium is the female reproductive organ which is a flask-shaped structure which is differentiated into two parts i.e. venter and neck. Venter contains egg cell and venter canal cell. A neck is comparatively longer and contains six or six to ten or more neck canal cells.
Antheridium is a globular structure without a stalk. There are 2 rings of cells and 1 cap cell which enclose many androcytes. Each androcyte metamorphosis into multi- flagellated antherozoid which comes through the opening of cap cell due to absorption of water.
Fertilization is the process of fusion of male and female gamete. Water is very essential for fertilization. During fertilization, the venter canal cells and neck canal cells degenerate and produce mucilaginous substance. Mucilaginous substance absorbs water swells up and gives pressure on the cover cell and cover cell separates apart.In this way, there is a formation of passage for the entry of antherozoids. Antherozoids are attracted towards archegonium by the chemicals coming out from the archegonium. Such type of movement of antherozoids towards the archegonium in response to chemicals is known as the chemotactic movement. Many antherozoids enter inside the archegonium but only one fuses with the egg cell to form the diploid zygote.
The zygote develops into the embryo and then in sporophyte. In this way, the lifecycle of Dryopteris continues.
The life cycle of fern plant shows alternation of generation. The main fern plant is sporophyte. The diploid sporophytic bears sporangia at the lower surface of leaflets. During asexual reproduction, sporangia produces many haploid spores, which germinates giving rise to the gametophyte, the prothallus. The prothallus bears male sex organ antheridia and female sex organ archegonia, which produce antherozoids and eggs respectively. Antherozoids and eggs fertilize with each other to form a diploid zygote which further divides to form the embryo that later develops into the sporophyte, the fern plant. Thus, the life cycle of fern shows a cyclic change from diploid to haploid generation and from haploid to diploid generation alternately.
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