BRYOPHYTES AND PTERIDOPHYTES

BRYOPHYTES  

“Bryon”-moss  “phyta” -plant. The bryophytes are the most primitive land plants. They are non-vascular mosses and liverworts that grow in moist shady region. They are called amphibians of the plants kingdom because these plants live on soil but Are dependent on water for sexual reproduction.

Characteristic features-

Habitat:- these Live in damp and shady habitats and are found to grow during rainy season on damp soil, rocks, walls etc.

The bryophytes consist of two generations. The gametophytic generation and a sporophytic generation. The gametophytic plant body is dominant, independent, haploid and long lived. It is concerned with the production of gametes.

The sporophytic plant body is diploid, dependent on gametophytic plant body and concerned with the production of spores.

Gametophyte;-

The plant body ranges from few millimeters (zoopsis)-70 cm (dawsonia)

The plant body is not differentiated into root stem and leaf.

Roots are absent but contain rhizoids.

Vascular tissue is absent however the cells that conduct water are termed as hydroids (xylem) and the cells that conduct food are termed as  leptoids (phloem).

Reproduction:- the reproduction occurs vegetatively by fragmentation.

The asexual reproduction occurs by special organs called gemma cups which detach from the parent body and develop into new plants.

The sexual reproduction is oogamous type. The male reproductive organs are called antheridia. Each antheridium consists of a stalk, and body. The body contains androcyte Mather cells covered by a layer of sterile cells called jacket. The androcyte mother cells undergo mitosis to produce biflagellated antherozoids (male gametes).

The female reproductive organs are called archegonia. Each archegonium consists of a stalk, Venter and neck. The Venter contains a large egg (female gamete).

The fertilization takes place in presence of water. The haploid egg and antherozoid undergoes fusion to produce a diploid zygote.

Sporophytic plant body:- the zygote acts as the first cell of sporophytic generation. The zygote divides and produces a large sporophytic plant body upon the gametophytic plant body. The sporophyte of bryophytes consist of a foot (it is parenchymatous and acts as an anchoring tissue), seta (it anchors capsule with foot) and a capsule. The      capsule is an oval structure consisting of a single layerd wall and the inner sporogenous tissue that contains spore mother cells. The capsule is also externally protected by calyptra. The spore mother cells undergo meiosis and produce haploid spores and elaters. The elaters are long tapering cells that are hygroscopic in nature and function in spore disposal.

Each spore consists of an outer rough covering called exine(sporopollinin) and an inner smooth intine (peptidoglycan). The spores germinate and produce new gametophytic plant bodies to complete their lifecycle.

• The Bryophytes are divided into two groups Hepaticopsida (Liverworts) and Bryopsida (Mosses).

Liverworts:-  “Hepatica”-liver shaped. The thallus is dorsoventraly flattened, dichotomously branched with or without leaf-like appendage.

The plant body consists of Unicellular rhizoids, multicellular scales and completely parasitic sporophyte or sporangium.

Asexual reproduction takes place by fragmentation of thallus or formation of specialized structure called gemmae. Gemmae are green, multicellular, asexual buds, which develops in small receptacles called gemma cups. The gemmae becomes detached from the parent body and germinate to form new individuals.

During sexual reproduction male and female sex organs are produced on same thallus or different thalli.

The sporophyte is differentiated into foot, seta and capsule. Common examples are marchantia, pellia, calobryum etc.

Mosses;-

The gametophyte of mosses consists of two stages- the first stage is protonema stage, which develops directly from spores and is a creeping, green, frequently filamentous structure. The second stage is the leafy stage, which develops from secondary protonema as lateral bud having upright, slender cal axis bearing spirally arranged leaves.

Vegetative reproduction occurs by the fragmentation and budding in secondary protonema. A sex organ develops on leafy shoots.

Sporophytes in mosses are more developed and consist of foot, seta and capsule.

Common examples are Funaria, Polytrichum, Sphagnum etc.

LIFE CYCLE

PTERIDOPHYTES;-

“Pteron”-feather “phyta”-plants. The Pteridophyts are feather like plants commonly known as ferns. These are primitive land plants with well developed vascular system. These were called as vascular cryptogams by linneus.

The Pteridophyts are an assemblage of flowerless, seedless, autotrophic, spore bearing vascular plants. Pteridophyts involve some oldest known vascular plants of the world like cooksonia (400 million years old).

General characters;-

Habitat;- these are terrestrial and mostly live in damp, shady conditions.

Plant body;- the main plant body is sporophytic plant body which is diploid and independent. It develops from the diploid zygote. The plant body is mostly herbaceous but some tree ferns are also found like cyathea spinulose, diksonia etc. the plant body is differentiated into root, stem and leaves.

Root;-  the primary root is short lived and is replaced by adventitious roots that arise endogenously.

Stem;- it is usually herbaceous. The stem is dichotomously branched.

Leaves;- the leaves are either small microphyllous or very large macrophylous.

Anatomy;- the stem and roots contain vascular tissue. The vascular bundles consist of xylem and phloem. The xylem consists of trachieds and xylem parenchyma. The vessels are absent. The phloem consists of sieve tube cells and phloem parenchyma. The companion cells are absent.

No secondary growth occurs in Pteridophyts.

Reproduction;-

The sporophytic plant body produces haploid spores. The spores are produced inside specialized reproductive organs called sporangia. .these sporangia may be produced in particular regions called strobilus or cones. Some Pteridophyts produce a single type of spore (referred to as homo-sporous) and most of them produce two types of spores microspores and megaspores (referred to as hetero-sporous). Each strobilus consists of many leaf like structures called sporophylls that bear sporangia. Each sporangium consists of an outer sterile jacket and an inner mass of spore mother cells. The spore mother cells undergo meiosis to produce haploid spores (in case of heterosporous microspores and megaspores are formed).

Gametophytic plant body;-

In Pteridophyts the gametophytic plant body develops from the haploid spores. It is haploid, dependent and concerned with the production of gametes.

A homosporous sporophyte produces a bisexual or monoecious gametophyte where as a heteosporous   produces a unisexual or diocious gametophyte. The gametopyte may grow within spore wall (such a development is called endosporic) or may grow on soil to form an independent plant body ( such a development is referred to as exosporic).

The sexual reproduction is oogamous type. The male reproductive organs are called antheridia. Each antheridium consists of a stalk, and body. The body contains androcyte Mather cells covered by a layer of sterile cells called jacket. The androcyte mother cells undergo mitosis to produce biflagellated antherozoids (male gametes).

The female reproductive organs are called archegonia. Each archegonium consists of a stalk, Venter and neck. The Venter contains a large egg (female gamete).

The fertilization takes place in presence of water how over the presence of water is not mandatory as in bryophytes. The haploid egg and antherozoid undergoes fusion to produce a diploid zygote. The zygote develops into a new sporophytic plant body.

Classification.

The Pteridophyts are divided into many classes by different taxonomists some important classes of Pteridophyts are Psilopsida (Psilotum), Lycopsida (Lycopodium, Selaginella), Sphenopsida (Equisetum), Filicopsida (Pteris, Adiantum)

LIFE CYCLE