- Occurrence: Its members are found in fresh water, stagnant ponds. They are attached to the bottom by rhizoids. They are found in warm and cool regions of temperate zone.
- Vegetative structure: The plant body shows complex structures. It has erect axis. This axis has nodes and internodes. Each internode conrists of single large elongated cell. But each node consists of a plate of small cells. Each node has two types of branches:
- Branches of limited growth: These are present in the form of whorl.
- Branches of unlimited growth: These are only one or more.
- Cell structure: Each cell has single nucleus. It has many discoid chloroplasts. Cell wall is composed of cellulose. A large number of crystals of calcium carbonate are also present in cellulose.
- Pigments: Pigments are chlorophyll a, chlorophyll b andXanthophyll. Reserve food material is starch.5. Asexual reproduction: Asexual reproduction by spore formation is absent. Vegetative reproduction occurs by special propagules. These are:
- Amylum stars: These are star shaped aggregates of cells. They are developed at the lower nodes.
- Bulbills: These are formed at the rhizoids.
- Protonemal outgrowth: These are also used for vegetative propagules.
6. Sexual reproduction: Sexual reproduction is oogamous. Plant may be monoecious or dioecious. Male sex organ is antheridia and female sex organ is oogonia. Both organs are enclosed by sheath of sterile cells. It forms male and female fruiting bodies. Thesr: bodies are called globule and nucule. Antherozoids are bfflagellated and coiled. Oospore produces filamentous protonema stage.
Chara is fresh water algae. It is submerged in ponds. It is attached to the muddy or sandy bottom by rhizoids. Sometimes, it grows deep underground. Mature plant is covered with calcium carbonate. Therefore, Chara is also known as stoneworts.
The plant body is erect. It has branched axis (stem like). It is attached to the substratum by rhizoid. The axis has nodes and internodes. Nodes: Each node has two types of branches:
- Branches of limited growth or leaves: Several braches of limited growth form whorl at nodes. Each branch has 3-8 nodes and internodes. After that their growth stops.
- Branches of unlimited growth: They may be one or more branches. They also arise from the nodes. Their growth continues with the growth of plant.
Intcroodes: Each internode is composed of single large cell. This cell is much longer. Internodal cell is covered by a single layer of cells called cortex. The cortical cells are elongated vertically but they have smaller diameter.
Young cells are uninucleate. They do not have vacuoles. The mature cells develop a large central vacuole. Its nuclei divide b. amitosis and it becomes multinucleate. Cells have many chloroplasts. These chloroplasts are spirally arranged in the peripheral portion of cytoplasm. Chloroplast contains pigments chlorophyll a, chlorophyll b and Xanthophyll. The reserve food material is starch. The cytoplasm shows cyclic moments.
Fig: Chara plant
- ft single dome shaped cell is present at the apex of branches. The apical cell divides and forms a new cell towards the posterior side.
- This new cell divides transversely. It forms upper and lower cells. The lower cell does not divide. It enlarges and elongates and forms internode. The upper cell divides vertically many times. It forms a plate of cells. The plate has two or more central cells and 1-6-20 peripheral cells. This plate forms node.
- Each peripheral cell of node divides and produces two cells. The outer cells act as apical cell of leaf. This apical cell divides to produce 3 to 8 cells and their division stops. It forms branches of Fmited growth (leaf). In some branches apical cell continue to divide and develop branches of unlimited growth. Some of the Izaf cells develop to form spine like appendages called stipules.
- The nodal cells of the leaves form cortical layer of internode. Upper half of cortical cell is derived from the upper node and lower part from lower node.
Fig: Growth in Chara
Chara reproduce vegetatively and sexually. Asexual reproduction by zoospore formation is absent.
Cha-a develops special vegetative propagules. These propagules detach from the plant body and develop new plant. These propagules are:
- Amylum star: These are star shaped group of cells. They are filled with starch. Amylum stars are produced on the lower side of the nodes.
- Bu’bib: Bulbils are produced on the rhizoids.
- Protonema outgrowth: These are formed on nodes.
Sexual reproduction is oogamous in Chara. Sex organs are antheridia and archegonia. They are enclosed by multicellular sheath. This sheath forms male and female fructification. The male fructification is called globule. The female fructification is called nucule.
The plants are homothallic. Both globule and nucules are borne on the node of the leaves. Nucule borne above the globule. A few species are heterothallic.
Fig: Reproductive organs of Chara
It is male fructification. Globule is ball like structure. Mature globule has yellow,or reddish colour. It is attached to the nodal cells by pedicel cells. Its wall is composed of eight shield cells. These cells are large and plat like. The outer wall of each shield cell has many radial ingrowths. So this shield appears multicellular. The centre of globule has eight cells called primary capitula. Primary capitula are attached with pedicel cells. Elongated manubrium cells attaeh the primary capitula with the inner surface of shield cells. Secondary capitals and tertiary capitals arise from the primary cap’tula. Several antheridial filaments are attached with the secondary capitula. Each cell of antheridial filament is antheridial proper. It is changed into single antherozoid.
A PORT1001 OF SPERMATOGENOUS
Fig: A: L.S of antheridium, B: Sperm, C: Sporogenous filament,
Development of globule
- Globule is developed from a single nodal cell. This cells present on the adaxial side.
- This nodal cell acts as apical cell. It divides to give two cells.
The lower cell divides many times to form node. The upper cell forms pedicel cell.
- The apical cell itself becomes rounded. Two vertical and one transverse division occurs in it. It produces eight cells or octant.
- The octants divide simultaneously. Each octant produces three cells. The outer most cells become shield cells. The middle cells become manubrium. The innermost cells become primary capitula.
- The shield cells expand laterally. It increases the size of globule. The manubrium cells elongate. Primary capitula give rise secondary and tertiary capitula.
- Primary and secondary capitula divide to give rise to antheridial filament. Each antheridial cells develops into antherozoid. Antherozoids are biflagellated coiled structure.
- Release of antherozoid: Antherozoids become mature. The shield cells separate from each other. It exposes the antheridial filament. A pore is formed in the antheridial wall. Antherozoid escapes from this pore. They swim in water.
Nuctile is a female fructification. It is composed of a large pedicel cell. Central and stalk cells are present on the pedicel cells. Oogonium is attached to the stalk cell. Oogonium contains single large oosphere. Oogonium is covered by five tube cells. These tube cells are elongated and spirally twisted. A crown of five cells is present at the top of oogonium. It is called corona.
Development of Nucule
- Initial cell of nucule is a nodal cell. This cell divides transversely
to produce row of three cells.
- The lowermost cell does not divide further. It forms pedicel cells.
- The upper cell becomes oogonial mother cell. Oogonial mother cells form a stalk cell at the base. Then it elongates and enlarges to form oogonium proper. It is changed into single oosphere.
- The middle cell divides to produce five peripheral cells and a zentral cell. The five peripheral cells enlarge to form tube cells. The tube cells spirally twisted around the oogonium and form sheath. Each tube cells cut off small cell at the tip. These cells form corona.
The nucule become mature. The tube cells separate from each other. It forms five slits. Antherozoids enter through these slits. One antherozoid enters into oogonium. It fuses with oosphere to form zygote. The zygote secretes thick wall and become zygospore. The inner wall of tube cells becomes thick. But the outer wall decay. The zygospore falls on bottom of the pond.
Fig: Stage of germination of Oospore
Fig: Life cycle of Chara
Germination of oospore
Germinationof zygospore migrates toward the apical pole of zygote. to four daughter nuclei by meiosis. The oospore divides into two unequal cells.
A small lenticular uninucleate cell is formed toward the tip. A large basal cell %%ith three nuclei is formed towards lower end. The zycospore wall breaks. The lenticular cell divides vertically into rltizoid initial and protonemal initial. The rhizoid initial forms rhizoid. Rhizoid develops nodes and internodes. The protonemal initial des clop into protonema. It also develops nodes and inttrnodes. Protontata gives rise to ne%‘ branches.
I. Occurrence: Mostly they are fresh water. Majority of them are found in stagnant ponds. Some grow on trees and damp walls. Some species are terrestrial. They grow in dry mud.
- Vegetative structure: The plant body may be unicellular or mul:icelltilar. Multicellular may be colonial or filamentous. Filament may coenocytic.
- Cell structure: Cell wall is chiefly r . used of pectic compounds Silica also adds in it. Most of them are uninucleate. Some coenocytes are multinucleate.
- Pigment: The cell have excessive amount of 13-carotene. So their colour is yellow green. Other pigments like chlorophyll r.. b and Xanthophyll are also present. Most of species lack pyrenoids. Reserve food material is leucosin. Starch is absent in them.
- Vegetative reproduction: Vegetative reproduction in filamentous form occurs by fragmentation. Unicellular forms divides by s’mple division.
- Asexual reproduction: They form one or more zoospores in each cell. Zoospore is biflagellate. The flagella have unequal length. The longer flagellum is tinsel type and shorter flagellum is whiplash type. Aplanospores are also produced in spine bacteria. Some species form endospores.
- Sexual reproduction: Sexual reproduction is rare in this group. Sexual reproduction is oogamous or sometime isogamous type. In case of oogamous, antheridia and oogonia are produced.