Describe briefly structure and life cycle of chara

Chara is aquatic attached to muddly or sandy bottom of the pools, lakes and slow flowing streams. Few species are marine. Plant body consists of an erect branched axis which may grow to 20-30 can. The axis has district nodes and internodes. From each node arise a whorl of laterals of limited growth called leaves. From the axis of some leaves branches of unlimited growth may arise. Each branch bears nodes and internodes. Plant is attached to substratum by colourless branched multi-cellular rhizoids which arise from lower nodes of axis.

Growth of axis in length takes place by means of single dome shaped apical cells. Each node has a plate of cells while inter-node consists of single elongated cells. Each cell has a cell wall made up of cellulose and deposit calcium carbonate. They contain a single nucleus, dense cytoplasm with many discoid chloroplasts.
Reproduction: In chara it takes place by vegetative and sexual method.

1. Vegetative reproduction: It takes place as under:

(i)         By amylum stars: Some of the cells of lower nodes form a mass of special type of cells which are star shaped and are called amylum starch as they contain amylum starch in their cells. They can give rise to new plant but their exact mode of development is not known.
(ii)        By bulbils: Some of the rhizoids or lower nodes may form bulbils which also give rise to new plants when detached.
(iii)       By Protonena formation: Some on the nodes protonena like branches are developed and they also form new plants.

2. Sexual Reproduction:

It takes place by male and female reproductive organs called globule (antheridium) and nucule (oogonuim). Mostly species are monoecious, a few may be heterothallic or dioecious.
Two structures are found just aposed at a node, nucule being above the globule.
Structure of Sex organs:

As we know the plant body of chara consists of main axis which bears nodes and internodes. From nodes arise branches of limited growth. This also possesses nodes and internodes. The sex organs are developed on the nodes of these branches. Structure of the globule or Antheriduim: Mature globule or antheriduim is circular in outline and red or orange in colour. Wall of globule consists of eight shield cells. Out wall of each shield cell is marked with many infolding giving the idea that wall of anteridium consists of more than eight cells but this in only apparent. From the centre of each shield cell there arise a rod like out-growth the manubrium which bears at its upper end primary capitytum cells which may form secondary and tertiary cells. Secondary capitulum cell bear, branched uniservate spermatigenous filaments which are divided into small segments by transverse septa. Each segment functions as a single antheriduim. Cytoplasmic contents of each segment give rise to single speematozooid or antherozoid. Each antherozooid is spirally coiled and biflagellate structure.

Development of Globule:

Globule like male reproductive organ arises in the axis of branches of limited growth from single superficial cell. This cell cuts off one or two discoid cell at its basal and then becomes spherical. The lower two cells form a pedicle while the upper cell enlarges in size and becomes hemispherical in shape. Upper spherical cell divides by two longitudinal and one transverse division to form octant (Scelled structure). This octant divides by two curved plates or shields) and form wall of globule. As the shield cells mature they develop red pigments and radial in growths. Middle eight cells elongate form a rod shaped manubrium which projects imvard from the centre of curved shield cells. Each of the inner eight cells becomes a primary capitulum borne at the tip of manubrium. Each primary capitulum buds off about 4 to 6 secondary capitulum cells which may further give rise of tertiary and quaternary ones. From each capitulum cell develop antheridial filament. Each antheridial filament consists of about 200 discoid cells the antheridia. Within each antheridium is produced single elongated spirally coiled and biflagellate antherozoid. When the globule or antheriduim is mature the shield cells fall apart and the antherozooids are liberated by gelatimisation of antheridial walls or through a pore formed in each antheridial cell.

Structure or Nucule or Oogonuim:

Nucule or Oogonium is short stalked body attached to the body of primary lateral or leaf or dwarf shoot or branch of limited growth just above the antheridium. A mature oogonium consists of a large oval or elliptical egg surrounded by a cover of five tubular cells which make two or more clockwise spiral turns around it. From the upper end of each of the tubular cells a cell is cut off forming the crown or corona of oogonium.
Development of Nucule:

Oogonuim or nucule, the female reproductive organ develops in the axil of the branches of limited growth on the ad axial side. It develops from single superficial ad axial cell. This cell under goes two divisions to form three cells. Lower neost cell elongates and forms pedicel, the middle cell gives rise to five peripheral cells and upper most act as oogoial mother cell. Each peripheral cell divides to form upper cell Corona cell and lower larger cell tube cell. Five Corona cells elongate many times become spirally coiled around oogonium. Nucule when mature, tube cells separate from one another below corona to form five small shits for entrance of antherozooids.

Fertilization: Tube cells of oogonium separate thus forms slit. Antherozoids enter by slits, only on succeeds in the formation of oospore or zygote.
Germination of Zygote: Zygote secretes a coloured wall around it and undergoes a period of rest within oogonium. It falls from plant sinks to bottom of pond where it germinates after few weeks.

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