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).