Sporophyte of the Funaria

                                    Funaria: The Sporophyte 

The mature sporophyte of Funaria consists of three different parts ie. foot, seta and capsule.

Foot: It is the lower most, small, pointed structure, remain embedded in the apex of female branch of the gametophore. It is the part of sporophyte which connects the sporophyte with gametophyte, at growing condition it helps to absorb water and nutrient from the gametophyte to supply to the sporophyte.  

Seta: It is the middle elongated, slender structure of the sporophyte. It connects the foot with capsule. It contains central core with elongated cells that continue till the bottom of capsule (apophysis), cortical tissue is the next surrounding to the core and cortex is surrounded by the outer epidermis. The main function of seta is to help in conduction of water and provide mechanical support to hold the capsule.

Capsule:  Capsule is the most important part of the sporophyte. It is the only-one fertile part out of the entire sporophyte. It is a large globose-pear shaped structure. Green at immature condition but become light green - brown at maturity.

The longitudinal section shows the following 3 zones in capsule,

a)      Apophysis

b)      Theca proper

c)      Upper region

a)      Apophysis:  It is the basal most part of the capsule. The central conducting strands of seta continues in the central region of the apophysis. This central strand region is surrounded by chloroplast bearing green spongy parenchyma tissue. The surrounding outer layer to the spongy tissue is one cell layer thick epidermis. Presence of stomata in epidermis is only found in apophysis region.

b)      Theca proper: It is the middle one region in between apophysis and upper region. This region has a complex tissue organization.

The central part of the theca proper is occupied by a sterile tissue mass, known as columella.

Next outer layer to the columella is a ‘U’ shaped spore sac carrying  sporogenous tissue which finally act or form spore smother cells, each spore mother cell divides to form 4 haploid spores.

Outside to spore sac the next part is composed of some elongated filaments (consists of row of cells) known as trabeculae, in between trabeculae air spaces are present.

Trabeculae filaments connect the inner spore sac to the outer spongy tissue layer (few cell layer thick).

Spongy tissue layer is surrounded by 2 cell layer thick hypodermis. The most outer layer is epidermis.

c)       The upper region: This upper region consists of the top most cap like structure known as operculum which is the covering structure on peristome teeth. Two whorl sets of peristome teeth are present here. The outer set of teeth has hygro-scoping  movement, whereas the inner set acts as a sieve to the spores during dispersal of spores.

The operculum is separated from theca region by a constriction. At inner side of this constriction a 2-3 layers of radially elongated cells are present called as rim or diaphragm. Outside to the diaphragm the next large, hygroscopically active ring of cells are found, known as annulus (helps in loosening of the operculum)

Dehiscence of the capsule and spore dispersal:

Sporophyte at  maturity and at the dry season starts the mechanism of capsule dehiscence and spore dispersal. At the dry season the operculam starts to shrive, in next the annulus layer swells up by absorbing air moisture. This unequal water content inside these two parts(operculum and annulus) causes break of the operculum through the annulus ring. Now the operculum layer become detached and thrown out from the capsule. In removing of the operculum the next two ring of peristome teeth become exposed. At this dry season the unequal shriving in spore sac and columella also causes to rupture the spore sac. The free spores now come out from the capsule through the elongated slits between the inner ring of peristome teeth (acts as sieve), this spore dispersal is promoted by the jerky movement of outer peristome teeth due to hygroscopic activity. Finally, the liberated spores are dispersed by wind.

Spore germination:

At favourable condition the spores germinate by formation of the filamentous non green protonema. This protonema then grows and being branched. Finally, the protonemal branches form short, green, erect chloronemal branches (forms the gametophore) and  downwards few branches form rhizoidal initials (forms rhizoids).

Reproduction in Funaria

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.

c)    Bulbil: Bulbils are the brown multicellular bodies  may be developed on the protonema and  rhizoids and germinates at proper condition to new thallus.

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.

Thallus structure of Funaria

                                         Funaria

It is the leafy bryophyta belongs to family funariaceae, order funariales and class music. The member is also known as Cord Moss(cord ie. rope like) , Little Goldilocks (golden hair like) etc.

The members of Funaria is a common terrestrial moss, commonly grow on moist ground and recently burnt lands (nitrogen rich soil ie. members are nitrophilous), on moist walls, crevices of rock, on tree trunks etc.

Plant structure:

The dominating plant generation is haploid gametophyte. The gametophyte has two phases ie,  a) A prostrate filamentous, ephemeral protonema and b) The erect, leafy and persistent gametophore.

The haploid spore germinates to a branched filamentous, prostrate, green protonema, on this protonema the erect gametophores are developed.

                                                The gametophore: 

Gametophore structure can be discussed under two points ie. morphology and anatomy,

Morphology:

The gametophore is about few cm. long (1-5), it consists of axis, leaves and rhizoids. 

Axis: The axis is slender, erect and branched. Branching is generally monopodial. The main axis and branches grow by terminal apical meristem cell.

Leaves: Leaves are ovate, green, sessile and develop spirally on the axis. The upper leaves are large and crowded and lower leaves are small and distant. Mature leaf has distinct mid rib.

Rhizoid: At the base of the axis, a lot of branched, multicellular rhizoids are available. The rhizoids are colourless or sometime brown in colour. The main function of rhizoid is anchorage the substratum and absorb water and nutrient. 

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Anatomy:

Axis or stem:

The transverse section of the stem or axis shows a very distinct layer of outer epidermis, middle cortex and central core. The epidermis is one cell layer thick, the cells are thin walled, small and contain chloroplast. Stomata is absent. Inside the epidermis, a multi layered cortex of parenchymatous tissues is present. It has two zones ie. outer thick-walled hypodermis tissue zone of 2-3 layered thick and inner cortex is multi-layered thin walled parenchymatous tissue zone. Young cortex bears chloroplast but mature one does not bear any chloroplast. Some times few leaf traces may also be found in cortex. The central core is composed of long, thin walled colourless parenchyma cells. This central core mainly helps in conduction of water minerals and organic food.

Leaves:

The cross section of the leaf shows a central multi cell layered, thin walled  mid-rib zone. The mid rib zone is conducting in nature. The wings of the lamina (leaf) are one celled thick and bearing chloroplast.

Sporophyte of Anthoceros

The zygote is the first cell that develop into sporophyte. The zygote inside the venter increases in size and divides repetitively by mitotic division to form a small embryo. Now the embryo continue its division and finally form an elongated sporophyte.

The sporophyte consists of a bulbous foot and a cylindrical, erect capsule (seta absent). In between foot and seta an intermediate meristematic tissue zone is present.

Foot: The foot is deeply inserted within the gametophytic tissue. this foot is made up of thin walled parenchyma cells. The main function of foot is to absorb water and nutrients from the gametophyte to supply to the capsule.
Meristematic tissue: The meristematic tissue is an unique feature of Anthoceros sporophyte, due to continue division of this tissue the capsule get elongated.

Capsule: The erect capsule is an elongated, slender,  cylindrical in structure. It may be of 2-3 cm, (in some species it may be up to more than 10 cm.) It looks like a horn or bristle, thats why the genus is known as hornwort.
The capsule has 3 distinct zones, ie. a) The central columella
                                                          b) The middle archesporium or sporogenous tissue zone
                                                          c) The covering wall layers

a) Columella: At the central portion of the capsule a cylindrical, supportive, pillar like tissue appearance is found, known as columella. It consists of 16 vertical rows of sterile cells. The main function of it is to provide mechanical support to the capsule.

b) Archesporium or sporogenous tissue: The surrounding of the columella the next tissue zone is known as archesporium, it mainly consists of sporogenous tissue. From the base to apex of the cpsule different stages of  development of spores from archesporium tissue are found.
At the very bottom of the capsule only single layer of archesporim cells are found, next upwards the other successive stages like spore mother cells, spore tetrad, free spores and pseudoelaters are found. Pseudo-elaters  are the multicellular elongated structures, help in spore dispersal. Here spore mother cells divide meiotically and form haploid spores.

c) Wall layers: Surrounding the sporogenous tissue zone the next outer covering layer is known as wall layers or jacket layers. This zone is multi layered (4-6), the most outer cell layer is epidermis, this epidermis layer is cutinised and carries stomata in place to place. The next inner layer to the epidermis is chloroplast bearing photosynthetic green tissue.

                                                          Capsule dehiscence: 

The dehiscence in capsule is apex to base orientation (basipetally). The dehiscence is usually performed  by two longitudinal dehiscence line. At maturity due to dehydration of the jacket layer, it starts to dehisce through the lines and form two valves of the capsule wall. Now the expossed inner mass of spores are being loosen by the hygroscopic movement of pseudo-elaters and air current helps indispersal of the spores.

                                                    Germination of the spore:

Under favourable condition the liberated spore germinates by formation of a germ-tube. The germ tube finally grows and form the young thalloid gametiphytic thallus of Anthoceros. 

Reproduction in Anthoceros

                                                     

Reproduction in Anthoceros is performed by all the three modes ie. vegetative, sexual and asexual.

Vegetative and sexual reproduction is found in gametophyte thallus, whereas asexual mode of reproduction (spore formation) is available in sporophye.

Vegetative reproduction:

a) Death and decay of older parts of the thallus causes separation of the terminal branches, these branches grow into new individual thallus.

b) Tuber formation is another option for vegetative reproduction in Anthoceros. Tubers are formed at the margin of the thallus, these tubers remain active even after death of the thallus and germinate into new thallus.in next favourable season.

Gemmae may be developed along the margin of the thallus in different species. It germinates after detachment from the thallus and forms new thallus.

Sexual reproduction: 

Anthoceros may be of monoecious (bisexual or homothallic) or dioecious (uni sexual or heterothallic). Monoecious species are generally protandrous (antheridia develop earlier than archegonia). Both the reproductive structures develop on the dorsal surface just behind the growing point of the thallus.

Antheridia: 

Antheridia may develop singly or in group(number may be varied) inside the antheridial chamber. A mature antheridium has a multicellular stalk and on he stalk the club shaped body is present. The body of the antheridium has a single cell layered jacket. The jacket is green in nearly mature condition but at full maturity it urns into red or bright ornage in colour. Inside the jacket mass of androcyte (antherozoid mother cell) cell are present. Each androcyte is metamorphosed into a single biflagellate antherozoid or sperm.

In presence of water the jacket of mature antheridium rupture at terminal position and the mass  of androcyte comes out. At final each androcyte forms a single antherozoid.

Archegonium: 

Archegonia are found on the thallus in embedded condition but the cover cells remain free on the surface. The mature archegonium consists of venter and neck but not surrounded by jacket layer (gametophyte tissue surrounds the structures), the neck has 4-6 neck canal cells, inside venter a ventral canal cell and a large egg is present. At the terminal of neck cover cells are found.

At maturity the cover cells disintegrate and the neck canal cell and ventral canal cell forms a mucilaginous matrix by interacting with water.

         

Fertilization:

Fertilization occur in presence of water. After formation of the mucilaginous matrix inside the archegonium, it comes out through the opened neck and form a mucilaginous mound. Antherozoids also migrate in presence of water and being attached to the mound, now the antherozoid enters through the neck and reach at venter to the egg.  Ultimately asingle antherozoid fuses with a single egg inside the venter and that how fertilization takes place. As a result of fertilization a diploid zygote is formed inside the venter.

Short note on thallus structure of Anthoceros

            Short note on thallus structure of Anthoceros

The genus Anthoceros is also known as hornworts due to to its appearance. It belongs to the family anthocerotaceae.

Habitat:
The member is cosmopolitan in distribution. The main availability e of the plant group is temperate and tropical region of the world. The best habitat for the members is mainly the moist shady places on soil, damp rocks, on woods etc.

Plant structure:
the main dominant plant body is gametophyte, latter on the sporophyte develops on the gametophyte.

Gametophyte plant body is discussed in two points ie. morphology and anatomy.

Morphology or external structure:
the plant body is dark green dorsiventral, prostrate thallus. The thallus is thick, variously lobed in margins and does not have any midrib. The dorsal surface of the thallus is smooth and the ventral surface has numerous smooth walled rhizoids. In the ventral surface some dark blue-green spots are found which represent the micro-colonies of Nostoc (a blue green algae).

Anatomy or internal structure:
Internal cellular difference is almost absent. in both the surface, the most outer layer is one cell layer thick epidermis. the epidermal cells are small sized with lens shaped chloroplast each having single pyrenoid.
The inside tissue to epidermis is not distinguished into individual photosynthetic and storage region. All the cells are parenchymatous having chloroplast with single pyrenoid. Cells are without any intercellular spaces.
Towards ventral region some intercellular cavities with mucilage are found, known as mucilage cavities. These cavities have minute openings at ventral surface known as slime pores, through these pores the blue green algae like Nostoc enters and starts to get colonized to form endosymbiotic relationship with the thallus.
On the ventral surface of the thallus  smooth walled  rhizoids are found. Reproductive units develop at the dorsal surface.