Q.What is Nucule?

The nucule is the female sex organ of Chara — an oogonium wrapped in a protective, spirally twisted jacket of sterile tube cells topped by a corona.

Chara (a green alga of class Charophyceae, sometimes called 'stonewort') has distinct, complex male and female reproductive structures borne on its thallus — the male organ is the globule (antheridium) and the female organ is the nucule (oogonium).

The nucule develops at the node, typically just below the globule. Structurally, it consists of:

• A single, large, ovoid egg cell (oosphere) at the centre.
• Enclosing it, five elongated tube cells that spiral around the egg cell in a left-handed twist, forming a protective jacket.
• At the top of these tube cells, a crown of small cells called the corona (usually five cells, sometimes in two tiers), which briefly open to allow the entry of the motile sperm (antherozoids) released from the globule, after which the corona cells close again once fertilisation occurs. …