Dahlgren (1940) noted that the nucellus sometimes becomes destroyed more rapidly at the sides of the embryo sac than at the proximal and micropylar ends.
In Pandanus (Pandanaceae), nucellar cells between the hypostase and the embryo sac enlarge and break off into the embryo sac, where they further divide (Fagerlind, 1940; Cheah & Stone, 1975).
The commonest condition for Lilianae (Rudall, 1994) is one where the proximal nucellus is short and broad, without enlarged dermal cells, but often with a hypostase and a fairly extensive subdermal region at the proximal ends around the sides of the embryo sac, but not towards the chalaza.
The hypostase is a well-defined group of cells immediately adjacent to the embryo sac (i.
It forms a barrier between the ovular vascular strand and the embryo sac, inhibiting the growth of the embryo sac into the chalaza (van Tieghem, 1901; Dahlgren, 1940).
A similar markedly enlarged proximal dermal layer, usually associated with large embryo sac nuclei, especially antipodals, also occurs in other members of the recircumscribed family Lomandraceae (Rudall & Chase, 1996; Chase et al.
In Lomandra the dermal cells adjacent to the embryo sac are transfer cells with relatively large surface projections, indicating a transfer of solutes.
Boesewinkel (1989) also considered these central cells in Drosera to be conductive, since they apparently form a conductive strand from the chalaza to the embryo sac.
However, as Dahlgren (1940) correctly observed, there is a critical difference between a postament, which is a resistant nucellar protuberance into the embryo sac (the lateral parts having often been eaten away), and a small resistant group of nucellar cells not projecting into the embryo sac, for which he proposed the term "podium.
Unfortunately, such work may not be possible to be developed in the case of in vivo androgenesis from the embryo sac, due to the difficulties imposed by its in vivo nature, within the embryo sac.
The indeterminate gametophytel gene of maize encodes a LOB domain protein required for embryo sac and leaf development.
Embryo sac development in the maize indeterminate gametophytel mutant: Abnormal nuclear behavior and defective microtubule organization.