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In this article we will discuss about:- 1. Characters of Bryophytes 2. Functions of Bryophytes 3. Economic Importance.
Characters of Bryophytes:
Bryophytes are nonvascular terrestrial plants of moist habitats in which z multicellular diploid sporophyte lives as a parasite on an independent multicellular haploid. Gametophyte that develops multicellular jacketed sex organs.
1. They have over 25,000 species.
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2. Bryophytes live in damp and shady habitats. They are often found to grow during rainy season forming green carpets or mats on damp soil, rocks, walls, tree trunks, etc.
3. The plants are small. They seldom attain great length or height, the maximum being 60 cm for a moss species growing in New Zealand.
4. The dominant phase or plant body is a free living gametophyte.
5. Vascular tissues are absent.
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6. Roots absent. Instead rhizoids occur. The latter may be unicellular or multicellular.
7. Accessory spores are not formed. Vegetative reproduction is quite common through fragmentation, tubers, gemmae, buds, adventitious branches, etc.
8. Sex organs are multicellular and jacketed.
They are of two types (Fig. 3.10), male antheridium and female archegonium. Antheridium produces a number of flagellate male gametes called sperms or anthropoids. Archegonium is flask-shaped with tubular neck and a swollen venter.
The single- layered wall of neck has 5-6 rows of cells. Internally it encloses a few sterile neck canal cells. The wall of venter is 1-2 layered. It encloses a venter cavity having a sterile venter canal cell and a fertile egg or oosphere.
9. The sterile internal cells of the archegonium (neck canal cells and the venter canal cell) degenerate and gelatinise. The gelatinous mass absorbs water and swells up into mucilage. The swelling mucilage opens the lid of the neck and creates a passage leading up to the oosphere. It possesses chemicals for attracting (chemo taxis) antherozoids.
10. An external layer of water is essential for the swimming of male gametes to the archegonia.
11. Fertilization produces an embryo inside the archegonium. The embryo grows into a sporophyte.
12. Sporophyte is parasite on gametophyte.
13. The sporophyte in bryophytes is also called sporogonium as it is attached and dependent on gametophyte. It produces haploid meiospores inside its capsule part.
14. On germination each spore produces a gametophyte either directly or through a juvenile filamentous stage called protonema.
15. Bryophytes show heteromorphic or heterologous alternation of generations.
Functions of Bryophytes:
Some of the important function of bryophytes are listed below:
1. Terrestrial Amphibians:
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Bryophytes are called terrestrial amphibians as they require an external layer of water on the soil surface for their existence.
The external water is required for:
(a) Dehiscence of antheridia and archegonia
(b) Swimming of male gametes to archegonia
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(c) Protection from transpiration and hence desiccation as the plant body is not covered by cuticle
(d) Supply of water to all parts through capillarity in the absence of vascular tissues.
2. Bryophytes do not Attain Great Heights:
Bryophytes seldom achieve great heights. They are small sized.
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The possible reasons are:
(a) Absence of roots,
(b) Absence of vascular tissues. Materials are transported from cell to cell,
(c) Absence of cuticle on the plant body.
(d) Absence of mechanical tissue,
(e) Requirement of external sheet of water for capillary conduction to all parts and transport of male gametes.
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Bryophytes are of three types—hepaticopsida (= hepaticae or liverworts), anthoceropsida (=anthocerotae or hornworts) and bryopsida (= musci or mosses).
3. Hepaticopsida (Liverworts):
The thallus is dorsiventral flattened, dichotomously branched with or without leaf-like appendages having unicellular rhizoids, multicellular scales and completely parasitic sporophyte or sporogonium. They occur on moist shady habitats like marshy ground, damp soil, water banks, deep in the woods, bark of trees, etc.
Examples:
Riccia, Marchantia, Porella, Pellia, Sphaerocarpos (Bottle Hepatic).
4. Marchantia:
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It is small dorsiventral flattened dichotomously branched thalloid plant with a length of 2-10 cm. Each lobe has an apical notch, a midrib and a dorsal groove. Upper surface bears polygonal areas (areolae), each with a ventilating air pore in the middle. They represent underlying air chambers having assimilatory or photosynthetic filaments.
Storage region occurs below it. Ventral surface bears two types of unicellular rhizoids and 4—6 rows of scales or amphigastria (on either side of midrib). The two types of rhizoids are anchoring smooth walled and capillary conducting tuber culate.
Vegetative reproduction occurs by fragmentation, progressive death of older parts, regeneration, development of adventitious branches and gemmae. Gemmae are small green, biscuit shaped stalked structures which are borne dorsally inside gemma cups. Mature gemmae separate and get dispersed by water and animals and germinate to form new thallus.
One gemma may produce two new thalli. Sexually, Marchantia is dioecious with sex organs borne on stalked upright receptacles or gametophores. Gametophore of male thallus is called antheridiophore having a stalk and a 8 lobed male receptacle. Each lobe of the male receptacle has alternate air and antheridial chambers arranged in acropetal fashion.
Each antheridial chamber has a single shortly stalked antheridium which produces a number of slightly curved rod shaped biflagellate spermatozoids or antherozoids or sperms. Gametophore of female thallus is called archegoniophore. Its receptacle has nine cylindrical processes or rays. The upper surface of female receptacle is convex and bears only air chambers.
Each lobe of the thallu receptacle has a patch of hanging archegonia on the under surface with younger archegonia towards the stalk and older archegonia towards the periphery. A two-lipped hanging membranous covering or perichaetium occurs around each archegonial patch.
The archegonium is shortly stalked flask-shaped structure having a cup-shaped perigynium around the base, a tubular neck and a swolthallus; B, Male thallus; C, Female lenventer. Neck has six rows of wall cells, four lid cells and 4—6 neck canal cells. Venter has single layered wall, a venter canal cell and an oosphere.
Sperms reach the open hanging archegonia by capillarity. They are attracted by proteins and K+ salts. Fertilization produces zygote which grows to form diploid sporophyte or sporogonium. Sporogonia are knobbed hanging structures covered by calyptra (from venter wall), perigynium and perichaetium. Each sporophyte or sporogonium has three parts— foot, seta and capsule.
Capsule has a single layered jacket. Internally the capable develops haploid spores and diploid elongated elaters. Seta elongates. Capsule is exposed and begins to dry up. Elaters undergo xerochasic twisting movements. Capsule breaks and spores fall down. They are dispersed by air currents. After falling down on a suitable substratum, each spore germinates to form a new thallus.
5. Bryopsida (Mosses):
They are foliose bryophytes having radial symmetry, multicellular rhizoids with oblique septa and a branched filamentous juvenile stage called protonema. Sex organs occur in clusters over the tips of branches. Sporophyte or sporogonium has a central columella, an assimilatory tissue and acellular peristome for helping in spore dispersal. Examples: Funaria, Poly trichum, Sphagnum.
Funaria:
It is a common moss of 3-5 cm in height that forms dense patches during rainy season. The plant has a radial symmetry with a once branched axis or stem, a number of spirally arranged leaves and branched colourless multicellular rhizoids.
Rhizoids have oblique septa. Main axis functions as male shoot while its branch which is extra axillary in origin, is female shoot. Later on female shoot overtops the male shoot. Leaves are crowded towards the apices.
Leaves have multi-layered midrib and single layered wings. Stem or axis has a single layered epidermis, multi-layered cortex and a central cylinder of colourless nearly empty cells called hydroids. Both stem and leaves of moss are gametophytic structures as compared to sporophytic structures of vascular plants.
Funaria multiplies vegetatively through fragmentation, formation of secondary protonemata, gemmae and tubers. Sex organs occur in male and female receptacles at the tips of male and female shoots respectively. The condition is known as monoecious and autoicous. The male receptacle is surrounded by a rosette of divergent perigonial leaves.
It is cup-shaped. Two types of structures occur in male receptacle, club-shaped stalked antheridia and knobbed or capitate green filaments called paraphyses. Female receptacle is covered by whorl of convergent perichaetial leaves. It contains stalked archegonia and pointed green filamentous paraphyses.
Sporophyte of Funaria has embedded foot, an elongated curved seta and a terminal pyriform asymmetrical capsule. Capsule has three parts— basal photosynthetic apophysis with central non-photosynthetic columella, middle spore producing theca (with central columella, an air space and small photosynthetic tissue) and upper lid or operculum separated from theca by large celled annulus on the outside and peristome on the inner side.
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Peristome consists of 32 a cellular teeth arranged in two whorls, outer hygroscopic and inner non-hygroscopic. As the spores mature, annulus shrivels and operculum falls down. Outer peristome teeth bend outwardly.
As the air shakes the capsule, the spores come out and are dispersed. Spores contain chloroplasts and have the ability to germinate immediately after falling on the suitable substratum.
Each produces a filamentous juvenile stage called pro tonema. Protonema has two types of branches, subterranean non-green rhizoidal and green epiterranean branches. Buds develop on green prostrate branches which grow to form new moss plants.
Economic Importance of Bryophytes:
Some of the major economic importance’s of Bryophytes are listed below:
1. Prevention of Soil Erosion:
Bryophytes, especially mosses, form dense mats over the soil and prevent soil erosion by running water.
2. Soil Formation:
Mosses are an important link in plant succession on rocky areas. They take part in building soil in rock crevices formed by lichens. Growth of Sphagnum ultimately fills ponds and lakes with soil.
3. Water Retention:
Dry Sphagnum can absorb 18—26 times its weight of water. This characteristic is employed by gardeners to keep seedlings and cut plants moist during transportation and propagation. In older times, Sphagnum moss was used in place of absorbent cotton.
4. Peat:
Sphagnum often grows in acidic marshes where there is little decay. The older dead parts of moss and other marshy plants are slowly carbonized, compressed and fossilized over thousands of years to produce a dark spongy mass called peat.
Peat is dried and compressed and cut to form blocks. The peat blocks are used as fuel. Peat is also good manure. It overcomes soil alkalinity and increases its water retention as well as aeration.
5. Other Uses:
Mosses are a good source of animal food in rocky and ice clad areas for mammals, birds and other animals. A decoction of Polytrichum commune was employed in removing kidney stones.
