Sexual reproduction in Funaria

Sexual reproduction in Funaria

Sexual reproduction in funerals monogamous type. The male reproductive organ is known as antheridium and the female reproductive organ is known as archegonium. They are borne in clusters at the tips of separate branches. They are autoecious.

Male branch and Antheridium

The male reproductive organ is known as antheridium. Antheridia are developed in a group at the apex of a male branch. The antheridia are surrounded by larger divergent peritoneal leaves. Perigonial leaves are larger than the vegetative leaves and give protection to the antheridia.

Antheridium is a club-shaped structure having a multicellular stalk. Antheridium is red or dark orange in color.The antheridium is covered with single layered sterile jacket layer inside which there is the development of astrocytes. Antheridia are intermingled with paraphyses. Paraphyses are multicellular filamentous cells with high sterile structure. Paraphyses give protection to the antheridia as well as they are photosynthetic in nature. Antheridium dehisces when opercular cells absorb water and disintegrates. Androcytes comes out from the antheridium and metamorphoses into biflagellated antherozoid i.e. male gamete or spermatozoid.

Female branch and Archegonium

Female branch develops from the lateral side of a male branch. Female reproductive organ archegonium is developed into groups at the apex of the female branch. The archegonia are surrounded by convergent perichaetial leaves which give protection. Archegonia are also intermingled with sterile, filamentous multicellular paraphyses.

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.The neck is comparatively longer and contains six or six to ten or more neck canal cells. The neck is closed with cover cells. The archegonia contain multicellular stalk. The archegonial jacket is singer layered in the neck region and double layered in venter region. Venter canal cell and neck canal cells degenerate and produce mucilaginous substance. Cover cells separate apart which makes a passage for the entry of antherozoids.

Fertilization

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 chemotactic movement. Many antherozoids enter inside the archegonium but only one fuses with the egg cell to form a diploid zygote.

Sporophyte

A zygote is the first cell of sporophytic generation. It develops into the embryo and then in sporophyte. It can be differentiated into three parts they are;

• Foot
• Seta
• Capsule

Foot

The foot is basal part of sporophyte which is made up of parenchymatous cells. It is attached to gametophyte and helps in absorption of nutrients from the gametophyte for developing sporophyte.

Seta

It is an elongated structure which connects foot and capsule.It also helps in conduction.

Capsule

The capsule is a highly organized pear-shaped structure with green color in young stage and orange or brown color at matured phase. Capsule can be divided into three parts they are;

Apophysis

It connects seta and capsule. The outer layer is called epidermic which contains small pores called stomata for gasses exchange. Inner of it lies spongy photosynthetic tissue which helps in the process of photosynthesis.

Theca

Capsule wall

It contains single layered epidermis. Inner of which lies hypodermis and spongy layer.

Airspace

Airspace contains air transverse by trabeculae i.e. multicellular photosynthetic filaments which connect spore sac with the spongy layer.

Spore sac

There is two spore sac. Spore mother cells are formed inside it which undergo meiosis cell division to form haploid spores.

Columella

Columella is the central part of theca which is made up of sterile parenchymatous cells. It provides nourishment for the developing spores.

Upper region

Calyptra is the uppermost part which is cap like structure and is blown away in dry condition. The operculum is the lid-like structure which is also blown away in dry condition. The peristome is hygroscopic in nature consisting of peristomial teeth in two rings, 16 teeth each. It looses water and opens out due to jerk and pressure inside it. Then bursting of spore sac and dispersal of spores take place.

Germination of spore

Spore is the spherical, haploid structure. Spore contains two layered wall outer layer is known as exine and the inner layer is known as intine. Spore is developed into protonema containing buds and finally, each bud can develop into new gametophytic plant body.

Alternation of generation in Funaria

The life cycle of funaria completes only when it passes through the gametophytic and sporophytic generations, which lie alternately to each other.The gametophytic funaria bears both male sex organ antheridia (club-shaped) and female sex organ archegonia (flask-shaped), which produce male and female gametes respectively. As antherozoid reaches the archegonia, antherozoids fuse with the egg to form a diploid zygote which represents the first sporophytic generation. The diploid zygote then develops into the sporogonium or sporophyte. The sporophyte can synthesize their food but it depends on gametophyte for the conduction of water and mineral salts. Here, sporophyte lives as semi- parasite. The body of sporophyte is differentiated into the foot, seta, and capsule.
The foot that remains embedded within the tissue of gametophyte acts as haustorium. Seta which is elongated, and slender conducts water and nutrients from foot and gives rise to the capsule. The capsule of sporophyte contains mother cells, which by reduction division produce haploid spores in the form of the tetrad, which instead of forming sporogonium develops into a haploid protonema that gives rise to leafy gametophyte. It represents the first cell of gametophytic generation, which is of longer duration and consists all the haploid structures. The sporophyte is of short duration and consists all diploid structures.