27 February 2021



Embryo sac with megaspore mother cell.

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The ovule shows stalk and body.
The body consists of integuments, nucellus and the embryo sac.
There are two integuments which form the outermost covering of the ovule.

Fig- showing 8-nucleate embryo sac

A small amount of nucellus is present between the integuments and the embryo sac.

Embryo sac is present deep into the tissue of nucellus.

Organised 8-nucleate Polygonam-type embryo sac has an egg apparatus, two polar nuclei and three antipodals.

Egg apparatus is situated at the micropylar end. It consists of centrally placed egg cell with two two synergids, one on each side of the the egg.
An egg cell has a large vacuole towards its micropylar end while synergids have a small vacuole toward its chalazal end.

Each synergids has a beak-like structure on its lateral side and filiform apparatus at its micropylar end.

Two polar nuclei are located in the centre of the embryo sac. These later fuse to form the secondary nucleus.

Three antipodal cella are located at the chalazal end. These degenerate soon, either before or just after fertilization.

Since this embryo sac develops from a single megaspore, it is known as monosporic, 8-nucleate Polygonam-type embryo sac.

Fig- Polygonam-type embryo development
Fig- structure of ovule

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