In a monosporic embryo sac development (Polygonum type), nuclear divisions are:
The mitotic divisions of the functional megaspore nucleus are strictly free nuclear, meaning nuclear division is not followed immediately by cell wall formation. Cell walls are laid down only after the 8-nucleate stage is reached, leading to the 7-celled organization.
Ref: Sequence showing 1 -> 2 -> 4 -> 8 nuclei stage before cell walls form.