Filiform apparatus is a characteristic feature of

$A$ : Tetraploid gametophyte can be produced from tetraploid sporophyte by means of apogamy.
$R$ : Apogamy involves fertilisation, not meiosis.

The pollination by the birds is called

The number of nuclei in a mature embryo sac are

Grass family (Poaceae) contains

Through which cell of the embryo sac, does the pollen tube enter the embryo sac