Pollen grains can be stored for several years in liquid nitrogen having a temperature of (in $^oC$)

$A$: Filiform apparatus guides the pollen tube into the synergids.
$R$: It is a special cellular thickening at the micropylar tip to secrete chemotropic stimulus.

At which temperature are pollen grains stored (in $^{\circ} C$)?

Intra-species incompatibility can be overcome by

Pollen tube at the time of entering the embryo sac has:

In the diagram given below,show the path of a pollen tube from the pollen on the stigma into the embryo sac. Name the components of the egg apparatus.