Ferm of Pteridium plant body has sporophytic phase of life cycle. Adult plant bears roots, rhizome and leaves. Rhizome arises on surface of soil and shows dichotomous branches and indefinite growth. From above surface of rhizome from nodes arise leaves and on lower surface the roots.
Reproduction: Ferm reproduces vegetatively and sexually.
Vegetative reproduction: It takes place by death and decay of older parts of rhizome. The branches on separation continue growth as independent individuals.
Sexual reproduction: It is highly advanced type. Sporophyte plant reproduces sexually by spores present in sporangium. Group of sporangi called sori remain present on lower side or ventral surface of leaf. Leaft containing sori is known as sporophyll. Sporangia bear only one type of spores i.e. the spores is homosporous. Sori are arranged on lateral veins or on margin.
Sporangium: Any cell of placenta or receptacle functions as sporangium initial cell. It divides into outer sporangial proper cell divides three diagonal wall to form pyramidal cell and it forms one celled thick wall of sporangium (capsule). Pyramidal cell divides in an outer jacket initial
And inner archegonium cell which forms outer layer of tapetum and innet mass of spore mother cells which undergo reduction divisiiion (Meiosis) and a nitotic divison to form four haploid spores frome each diploid spore mother cell.
Mature sporangium of ferm (Pteridium) is club shaped with long slender multicellular stalk and a capsule with jacket layer of annulus and stomium and spores inside.
Dehiscence of sporangium:
On maturity of sporous the inducium deries exposing the sporangia to dry air. The wall of sporangium begins to lose moisture and dry up. The annulus strengthens and is doing so the sporangium open and the spores get liberated free.
The Gametophyte:
Spore is the unit of gametophyte. The spores of Pteridium or any other ferm are all alike i.e. homosporous and haploid. Eahc spore has two wall layers, a thin endospore (intine) and a hard brown thickened expore (exine). In the centre of spore are haploid nucleus and some cytoplasm around it.
At the time of germination of spore the exine ruptures and intine forms tubular structure. This divides into unequal cells, lower cells form rhizoid, and upper green cell divides to for a massive heart shaped prothallus.
This prothallus leads an independent life and it is on this that the sex organs develop.
Thus the mature gametophytes of ferm are a thin green flat mass of tissue and on underside of prothallus slender rhizoids grow out from cells. There is single nucleus and large number of chloroplasts in each cell of prothallus.
Development of antheridium:
Male reproductive organs of Ferm are antheridium and develop on lower side of prothallus near rhizoids. Any cell from lower surface of prothallus functions as antehridial initial cell and it directly develops into antheridium. Upper cell divides into done cell and a primary andrognial cell. Done cell divides to from second ring cell and cover cell and they form jacket of antheridium, Primary andrognial cells divide to form androcytes which get metamorphosed into uninucleate and multinucleate antherozoid.
On maturity of antheridium when water is available ring cells swell up and put pressure to open cover cell and antherozoids come out.
Development of Archegonium: They are female organs which develop near the notch of prothallus. Any cell of it functions as archegonial initial cell. It increases in size and divides into three cells out of which only upper or primary cover cell or venter take part
In further development. Primary cover cell divides to form four rows of neck cells, while the central cell forms a binulceate neck canal cell. Venter canal cell and a large egg. The neck archegonium is curved towards the posterior end. Thus the archegonium is flask shaped.
Fertilization:
Water medium is essential for fertilization. When archegonium is mature, nedck canal cell and venter canal cell disorganise and a passage is formed to enter the antherozoids, which reach the neck of archegonium. Fusion of one antherozoid nucleus takes place with egg of archegonium which results in formation of oospore or zygote which is diploid in nature.
Sporophyte: Zygote is first cell of sporophyte. After fertilization the zygote enlarges inside the venter of archegonium. Zygote divides into epibasal and hypobasal cell, one more divison taks plae to form four cells which further divide into eight and redivides to form multinucleate embryo. Half epibasal cells form stem and leaf, half hypobasal cells form root and foot. By further growth in embryo forms sporophytic plant which soon separates from prothallus and becomes independent plant. In this way life history of ferm shows distinct alternation of generation from sporophyte to gametophyte.
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