The cell closest to the chalaza becomes the functional megaspore (FM). The three non-functional megaspores (dm) degenerate shortly after meiosis.

Which end megaspore remains functional?

Reason: In monosporic (Polygonum) type of embryo sac development, usually the megaspore which is situated towards micropylar end remains functional.

How many megaspores are functional?

The megaspore mother cell undergoes meiosis and forms four megaspores. Three of the megaspores undergo cell death. The chalazal-most megaspore survives, becomes the functional megaspore, and undergoes megagametogenesis.