Nitella

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Nitella:-
1. Classification:-
Division:- Charophyta
Class:- Charophyceae
Order:- Charales
Family:- Characeae
Genus:- Nitella
2. Habit and Habitat:-
> Nitella cosmopolitan, present in fresh or slightly brackish water; endemic species present on all continents (except Antarctica). 
> Unisexual species tend to be endemic; bisexual species more widely distributed. 
> Oospores of N. furcata with temperature dependent annual cycle of germination. 
> Subfossil oospores can be identified from lake sediments. 
> Nitella used as a model system for studies of cytoplasmic streaming, and cell wall synthesis.
3. Thallus structure:-
> Mature plants 30-100 cm height, attached with numerous basal rhizoids, these multicellular, colorless and branched. 
> Primary axes with alternating sequence of nodal and internodal cells developed from apical cell. 
> Each apical cell derivative divides transversely and the daughter cells develop into multicellular nodal complex with 6 (rarely 7-8) peripheral cells, and its internodal cell, respectively. 
> Each peripheral cell divides periclinally; the inner cell develops into a basal node, whereas the outer becomes an apical cell and produces the branchlet; stipulodes absent. 
> Each node with whorl of four to many determinate, ecorticate branchlets. Branchlets furcate, with sympodial growth, appearing di- or trichotomously branched to 3-4 orders, with acuminate branch tips. 
> Indeterminate axes up to two or more per node, developing in axils of branchlets and scattered on plant. 
> Cortication on internodal cells absent. 
> Cytoplasm distinctly layered with external stationary layer with rows of helicoidally aligned chloroplasts (ectoplasm) and internal streaming layer with nuclei, mitochondria (endoplasm); cells with large central vacuole. 
4. Reproduction:-
> Sexual reproduction oogamous with gametes produced in multicellular gametangia. 
> Species uni- or bisexual, in former antheridia single and terminal at point of furcation, oogonia lateral and subtending furcation. Antheridium is called globule and oogonium is called nucule.
> In bisexual species antherida as in unisexual forms with one to several oogonia subtending node. 
> Antheridia similar to Chara except for presence of two rather than one stalk cell, developing from terminal cells of branchlets. 
> Antheridial stalk cells formed after the development of antheridial mother cell. 
> Sperm released from antheridial filament by pore in cell wall; pore more specialized than in Chara. 
> Oosporangia encrusted with calcium carbonate, with two, 5-celled tiers of crown cells; at maturity compressed laterally. 
> Oosphere with three sterile cells. 
> Zygote germination associated with development of protonemal stage that undergoes divisions to form large and small cells. 
> The primary axes develop as lateral branches to the protonema.