BRYOPHYTA BIOLOGY NOTES
Bryophyta is a group of higher cryptogams in which the plant body may be thalloid(primitive forms) or leafy (advanced forms). They may develop some root like structures called rhizoids but true root and vascular tissues are absent. Bryophytes are known as amphibious of plant kingdom because they grow on moist habitat. It is divided into three classes:
- Hepaticeae e.g. Marchantia
- Anthocerotae e.g. Anthoceros
- Musci e.g. Funaria
Marchantia Life Cycle
Division : Bryophyta
Class : Hepaticeae
Order : Marchantiales
Family : Marchantiaceae
Genus : Marchantia
Marchantia is cosmopolitan genus, grows on damp wall and moist ground. The gametophytic plant body is prostrate, dorsivertral and dichotomously branched. The ventral surface of thallus possess a multicellular scales. The rhizoids are of two types : Smooth walled and tuberculate. Thizoids help in absorption and fixation. Scales are also of two types : Ligulate and appendiculate. Scales protect the thallus from mechanically injury and desiccation. The dorsal surface bears a number of cups like outgrowths known as gemma cups on the midrib. The gemma cup bears gemmae which help in vegetative reproduction. The gemma has an isobilateral, multicellular body having one celled stalk. The gemma when mature comes out from the cup and comes in contact with soil. The growing point seated near each notch, hence two thalli produced from each gemma after death and decay.
Internal Structure of Marchantia
The v.s. of thallus shows three distinct layers: epidermal region, photosysthetic region and storage region. Epidermal region consist of upper and lower epidermis. It consists of single layer of thin walled cells with number of air pores. Photosysthetic region made up of air chamber on which photosynthetic filaments develop. Storage region consist of compactly arranged parenchymatous cells rich in starch and protein. This region is followed by lower epidermis which gives rhizoids and scales.
Reproduction in Marchantia
It reproduces vegetatively by means of:
- Progressive death and decay of older parts i.e. fragmentation.
- Adventitious brances develop on ventral surface of thallus.
- By gemma present on the dorsal surgace.
Sexual reproduction is oogamous type. Marchantia is a dioecious plant. Sex organs are present on the receptacle of upright branches called gametophores. The antheridia develop on antheridiophore and archegonia develop on archegoniophore. Each antheridiophore internally consist of air chamber and antheridial chamber. An antheridial chamber consist of a stalked antheridium. The antheridium consist of stalk and globular body composed of a mass of antherezoids mother cells which develops the male gametes (antherezoids and spermatozoids). Internally archegoniophore posses stalked archegonia. The archegonium consists of a long stalked archegonia. The archegonium consists of a long stalk and flask shaped body with tubular neck and swollen basal venter. Venter posses egg cell and venter canal cell.
The antheridium brust on maturity and antherezoids escape out through ostiole and reach to the archegonium and enters in the venter. But only one of them fuses with egg cell to forms the zygote. The zygote later give rise to sporophyete (Sporogonium). It consists of foot, seta and capsule. Foot absorbs nourishment from gametophyte for developing sporophyte. Seta connects the foot to capsule. Capsule consists of elaters mother cells and spore mother cells. Spore mother cells undergo reductive cell division and forms four spores in a tetrad. Elaters absorb water and nourishment for spores and help in dispersal of spores by its hygroscopic movement. Later on capsule dehisces and spores discharge. The spores under favorable condition germinate and give rise to Marchantia thallus. One half of the spores give rise to male thalli and another half to female thalli.
Alternation of Generation in Marchantia
The life cycle of Marchantia shows two stages: Gametophytic and Sporophytic. The plant body is gametophyte (n) and sporogonium is the sporophyete (2n). The gametophyte reproduces sexually by gametes which produce on multicellular sex organs and produce zygotic structure called oospore (2n). Oospore is the first sporophytic structure which grows and gorm sporogonium. In the capsule of sporogonium, number of mother cells undergoes meiosis and forms haploid spores. The haploid spores germinate and give rise to the gametophyte. Thus, two generations regularly alternate with each other known as alternation of generation.
FUNARIA Life Cycle
Funaria is the moist loving plant grow on rock, moist ground, walls, tree trunk etc. plant body is foliose and differentiated into rhizoids, stem and leaves. The plant body gametophyte consists of a small, erect axis surrounded by spirally arranged minute sessile leaves and numerous rhizoids at base. The axis may be branched or unbranched. The branching is lateral type. True roots are absent and rhizoid perform the function of root i.e. absorption and anchorage.
Internally, it consists of 3 parts: epidermis, cortex and central cylinder. Epidermis is the outer most covering contains chloroplast but lacks cuticle and stomata. Cortex lies inner to the epidermis, made up of several layer of cells with chloroplast. Central cylinder lies in the center which consists of thick walled cells and helps in conduction of water and nutrients and also provides mechanical strength.
Reproduction in Funaria
The plant reproduces vegetatively and sexually. The vegetative reproduction takes place from:
- Death and decay of rhizoids.
- Bulbils (fleshy buds) present on rhizoids.
- Apospory, development of gametophyte directly from the vegetative cells of the sporophyte.
- Multicellular structure of gemmae produced on protonemal branch.
- Primary and secondary protonema.
The branched, multicellular and filaments primary protonema develops from germination of spore which consists of many buds. Each bud later on develops into new plant. The protonema develops from any parts of the plant except spore is called secondary protonema, which also possess buds, that on germination give rise to new plant.
Sexual reproduction in Funaria
Sexual reproduction is oogamous type. Funaria is a monoecious plant i.e. male and female sex organs are developed on the same plant, but in separate branches (autoecious). The antheridia develop on the apex of the main axis (antheridiophore) then archegonia develop on the summit of archegoniophore, arise from the lower portion of main axis. Funaria is protandrous i.e. antheridia develop first then archegonia and ensures cross pollination.
The apex of male branch bears antheridia intermixed with paraphyses in a cup like structure covered by perichaetial leaves. The antheridium consists of multicellular stalk and club shaped body. It possesses the antherezoid mother cells (androcytes). Each androcyte differentiate into a single spirally coiled biflagellated antherozoid. Archegonium consists of a multicellular stalk and flask shaped body, differentiated into narrow neck and venter. Neck possesses the neck cells and neck canal cells and venter possesses the venter cell and an egg cell. On the maturation the neck canal and venter canal cells disintegrate.
During the course of fertilization, many antherezoids reach to the neck of Archegonium with the help of water but only one of them fuses with egg to form zygote. Then is secretes a wall and becomes oospore. The oospore grows in situ and gives rise to sporophyte (sporogonium).
Sporogonium is differentiated into foots, seta and capsule. Foot is poorly developed and absorbs nutrients and water from the gametophyte. Seta is long, stalks like structure possess central cylinder and joins the capsule to the foot.
Capsule is differentiate into three distinct regions:- Apophysis, Theca proper and apical region. Apophysis is sterile, basal portion of a capsule possesses central cylinder of parenchymatous cells, covered by the outermost layer epidermis.
Theca proper is a central fertile portion of capsule; possesses capsule wall, air space, spore sacs and columella. The two spore’s sacs, one on either side of collumella, possess a number of haploid spherical spores by meiotice division. Apical region consist of operculum and peristome. The operculum is lid which closes the mouth of capsule. Beneath the operculum lies the two sets of teeth (each possesses 16 teeth) known as inner and outer peristome.
At maturity the annulus cells break and the operculum is removed. Thus after the dehiscence of capsule haploid spores are released under favorable condition the spore germinate. The exosporium brust and endosporium comes out in the form of germ tube, which give rise to multicellular septate, filamentous protonema. It possesses two types of branches: chloronemal branch and colorless rhizoidal branch. The chloronemal branches give rise the leafy gametophores.
Alternation of generation in Funaria
Two distinct gametophytic and sporophytic generations are present alternating with each other in the life cycle of Funaria known as alternation of generation. The plant body is gametophytic (n) produces male and female gametes, which fuse to form diploid structure inside capsule. Later it gives rise to gametophyte and completes in life cycle.
Economic importance of bryophyta
- Bryophytes help in soil conversation. They bind the soil particles and prevents soil erosion by running water.
- They are useful in formation of soil. They grow on rocks and add organic matter to the substratum after their death.
- They are good source of manures.
- They are very useful in moistering plants.
- Certain bryophytes are used to obtain a number of antibiotics.
- Some bryophytes are also known as indicator of pollution.