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The structure of the proximal end of the nucellus, adjacent to the chalaza, is variable and often includes modifications such as a hypostase or enlarged dermal cells.
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.
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).
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.
This is a vascularised region formed by proliferation of the chalaza, which becomes enclosed by the nucellus after fertilisation, as a result of campylotropous curvature.