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General characters of Pteridophytes Posted on : 24-11-2017
Posted by : Admin
Pteridophytes are vascular cryptogams. They occupy the position between bryophytes and Spermatophytes. They are chlorophyllous, autotrophic, archegoniate, embryophytic and tracheophytic. Pteridophytes show diplohaplontic life cycle.
General characters of Pteridophytes
These are the first true land plants in the evolution of the plant kingdom.
Pteridophytes exhibit a well-defined heteromorphic alternation of generations. Diploid sporophyte is the dominant phase in life cycle.
Sporophyte is an independent plant and is free from gametophyte at maturity.
Gametophyte is either fully or partially dependent on sporophyte for its nutrition.
Sporophyte is differentiated into stem, root and leaves.
Pteridophytes have an internal conducting system consisting of xylem and phloem. They are the only vascular cryptogams.
The roots of Pteridophytes are adventitious type.
The stem of Pteridophytes is usually a rhizome. But in Lycopodials and horse tails the stem is aerial.
The leaves are small (microphyllous) in several groups of plants and in higher forms they are large (Macrophyllous) and simple with well-developed petiole.
Asexual reproduction is by spores. Sporophyte produces meiospores inside a little capsule called sporangia. The sporangia are borne on the lower surface or in the axils of fertile leaves called sporophylls. It may be homosporous (spores produced are of only one type) or heterosporous (spores produced are of two types).
The spores germinate to produce a haploid gametophyte called prothallus. Homosporous species usually produces bisexual (monoecious) gametophytes whereas heterosporous species produce unisexual (dioecious) gametophytes.
The microspore germinates to produce male gametophyte and the megaspore germinates to produce female gametophyte. Gametophyte performs sexual reproduction by zooidogamous type of oogamy
Sex organs (both antheridia and archegonia) are multicellular with a sterile jacket but without stalks
Fertilization takes place in the venter of archegonium. Water is necessary for it.
The diploid zygote develops into embryo in the archegonial venter. The embryo grows into sporophyte.
The life cycle of Pteridophytes is diplohaplontic with heteromorphic alternation of sporophyte and gametophyte. Sporophyte and gametophyte are independent of each other.
Development of sporangium
Development of sporangium may be of two types namely,
Leptosporangiate: Sporangium develops from a single superficial cell
Eusporangiate: Sporangium develops from a group of superficial cells